Hydraulically Driven Working Vehicle and Hydraulic Transaxle

ABSTRACT

In a hydraulic four-wheel drive vehicle, a rear transaxle incorporates a hydraulic motor for driving rear wheels, a front transaxle incorporates a hydraulic motor for driving front wheels, and hydraulic pressure fluid pipes interposed between the front and rear transaxles are extended along at least one of left and right side plates of a frame of the vehicle.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of application Ser. No.11/402,101, filed Apr. 12, 2006, which is hereby incorporated in itsentirety herein by reference thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a hydraulically driven working vehicle,especially, a four-wheel drive working vehicle, equipped with frontwheels and rear wheels driven by respective hydraulic motors, andrelates to a hydraulic transaxle including the hydraulic motorapplicable to the vehicle. An example of the hydraulically drivenworking vehicle according to the invention is a lawn tractor equipped atthe middle body portion thereof with a mower unit. The transaxleaccording to the invention can supply fluid to hydraulic equipmentsequipped on the hydraulically driven vehicle, e.g., a hydraulic powersteering system, in addition to the hydraulic motor for driving an axle.

2. Related Art

Conventionally, there are well-known hydraulic four-wheel drive workingvehicles, each of which is equipped with front and rear hydraulic motorsfor driving front wheels and rear wheels. A hydraulic four-wheel driveworking vehicle, as disclosed in International Publication No.2004/062956, is provided with a rear transaxle including a hydraulicmotor for driving left and right rear wheels, and with a front transaxleincluding a pair of left and right hydraulic motors for drivingrespective left and right front steerable wheels. This type hydraulicfour-wheel drive working vehicle is equipped at a middle portion thereofbetween the front and rear transaxles with a traveling powertransmission system for transmitting power from a prime mover to therear transaxle, and with a working power transmission system fortransmitting power from the prime mover to a working device. In thissituation, the front and rear transaxles are fluidly connected to eachother via pipes for driving the front and rear wheels (axles), and theaxle-driving pipes have to be disposed at the middle portion withoutinterfering with the traveling power transmission system and the workingpower transmission system.

To miniaturizing the hydraulic four-wheel drive working vehicle, thepipes are requested to be disposed within a space inside a vehicle bodyframe. However, the space is mainly occupied by the traveling powertransmission system and the working power transmission system. Further,the vehicle may be equipped under the fore-and-aft middle portion of thevehicle body frame with a working device, such as a mower unit.

The axle-driving pipes have to be disposed in the space between thefront and rear transaxles without interfering with the traveling powertransmission system and the working power transmission system, and theworking device at need. Further, to facilitate assembly works, the pipesare desirably disposed so as to require no device to be detached duringthe piping work of the pipes, and to require no pipe to be detachedduring attachment of other devices. On the other hand, in order toreduce internal pressure resistance in the pipes, the pipes arerequested to have reduction of bent portions therein and to have rigidpipe portions as long as possible. Especially, the pipes have to beprevented at portions thereof adjacent to a center pivot of the fronttransaxle with being excessively twisted or bent, and prevented atportions thereof connected to ports from having oil leak or beingdamaged.

If the hydraulic four-wheel drive vehicle includes a hydraulic powersteering system, hydraulic fluid pipes for the power steering systemmust be disposed so as to solve the same problems as the axle-drivingpipes.

Further, if the vehicle is provided with a reservoir tank for supplyingfluid to the hydraulic motors in the front and rear transaxles, it isrequested that the reservoir tank is disposed so as to be prevented frominterfering with the traveling power transmission system and the workingpower transmission system, to have easy oiling and maintenance, and toeffectively supply fluid into the housings of the front and reartransaxles. Especially, when the front transaxle housing is swingablysupported onto the vehicle body frame via a center pivot, the reservoirtank is requested to prevent fluid therein from being contaminated withair by tilt of the fluid level surface according to the swing of thefront transaxle housing, and to prevent hydraulic pressure fluid pipesbetween the reservoir tank and the transaxles from being twisted by theswing of the front transaxle housing.

SUMMARY OF THE INVENTION

A first object of the invention is to provide a hydraulic four-wheeldrive working vehicle with a simple hydraulic pressure piping structuresolving the above problems.

To achieve the first object, in a first aspect of the invention, ahydraulically driven working vehicle comprises: a frame including a pairof left and right side plates extended in the fore-and-aft direction ofthe vehicle; a first transaxle supported by one of front and rearportions of the frame, the first transaxle including a hydraulic pump, afirst hydraulic motor fluidly connected to the hydraulic pump, a firstaxle driven by the first hydraulic motor, and a first transaxle housingincorporating the hydraulic pump, the first hydraulic motor and thefirst axle, wherein the first transaxle housing is provided with a pairof outwardly opened first ports fluidly connected to the hydraulic pumpand the first hydraulic motor, respectively; a second transaxlesupported by the other rear or front portion of the frame, the secondtransaxle including a second hydraulic motor fluidly connected to thehydraulic pump, a second axle driven by the second hydraulic motor, anda second transaxle housing swingably supported on the rear or frontportion of the frame through a center pivot, and incorporating thesecond hydraulic motor and the second axle, wherein the second transaxlehousing is provided with a pair of second ports fluidly connected to thesecond hydraulic motor; a prime mover supported by the frame between thefirst and second transaxles; a traveling power transmission systemsupported by the frame between the prime mover and the first transaxleso as to drivingly connect the hydraulic pump to the prime mover; aworking device disposed under the frame between the first and secondtransaxles; a working power transmission system supported by the framebetween the prime mover and the working device so as to drivinglyconnect the working device to the prime mover; and a pair ofaxle-driving hydraulic pressure fluid pipes interposed between the pairof first ports and the pair of second ports so as to fluidly connect thesecond hydraulic motor to the hydraulic pump. The pipes includerespective fore-and-aft extended portions which are extended in thefore-and-aft direction of the vehicle between an inside surface of atleast one of the left and right side plates of the frame and thetraveling and working power transmission systems.

In the vehicle according to the first aspect, the axle-driving hydraulicpressure fluid pipes disposed so as not to be exposed sideward from theframe vehicle, thereby being protected from external obstacles.Consequently, the traveling performance of the vehicle can be safelymaintained. Further, the vehicle has good appearance because of thehidden pipes.

In the vehicle according to the first aspect, preferably, thefore-and-aft extended portions of both of the pipes are extended alongthe inside surface of one of the left and right side plate. Due to thesimple arrangement of the pipes in the narrow space along the insidesurface of the side plate, the vehicle can be minimized while ensuringprevention of the pipes from interfering with the traveling and workingpower transmission systems and the working device. Further, the pipingwork for this arrangement of the pipes can be easy.

Alternatively, in the vehicle according to the first aspect, preferably,the fore-and-aft extended portion of one of the pipes is extended alongthe inside surface of one of the left and right side plates, and thefore-and-aft extended portion of the other pipe is extended along theinside surface of the other right or left side plate. Due to the simplearrangement of the pipes in the narrow spaces along the inside surfacesof the side plates, the vehicle can be minimized while ensuringprevention of the pipes from interfering with the traveling and workingpower transmission systems and the working device. Further, the pipingwork for this arrangement of the pipes can be easy.

Further preferably, at least one of the pipes includes: a first rigidpipe portion connected to one of the first ports; a second rigid pipeportion connected to one of the second ports; and a flexible pipeportion interposed between the first and second rigid pipe portions. Theflexible hose is extended along one of the left and right side plates ofthe frame. Therefore, the flexible hose can be bent or curved so as toabsorb stress on the pipe according to the swing of the second transaxlearound the center pivot. Consequently, the at least one pipe can bedurable against the frequent swing of the second transaxle.

Alternatively, preferably, at least one of the pipes includes: a rigidpipe portion connected to one of the first ports and extended along oneof the left and right side plates of the frame; and a flexible pipeportion interposed between the rigid pipe portion and one of the secondports. Consequently, the main portion of the at least one pipe is therigid pipe portion whose internal pressure resistance is small so as toensure good fuel efficiency.

In either of the above two cases where the at least one pipe uses therigid pipe portion, preferably, a stay is supported on either the firsttransaxle housing or one of the left and right side plates of the frameso as to support the rigid pipe portion connected to the first port.Therefore, the stay prevents warp of the pipe caused by the swing of thesecond transaxle around the center pivot from being transmitted to theend of the pipe connected to the corresponding first port, therebypreventing the pipe end and the first port from having oil leak and frombeing damaged.

Further preferably, the first transaxle housing includes a bossconnected to the frame, and the stay is mounted onto the boss.Consequently, due to the support by the stay on the first transaxlehousing, the pipe end and the first port connected to each other arefurther surely prevented from moving relative to each other causing theoil leak and damage. The boss ordinarily formed on the first transaxlehousing serves as a fixture portion onto which the stay is fixed,thereby requiring no additional fixture member and saving costs.

Further preferably, the at least one of the pipes further includes aswivel joint disposed between the flexible pipe portion and at least oneof the first and second rigid pipe portions. The swivel joint absorbstwist of the pipe caused by the swing of the second transaxle around thecenter pivot, thereby inexpensively providing the pipe having highdurability against the swing of the second transaxle.

Alternatively, in the vehicle according to the first aspect, preferably,the pair of first ports are disposed at one of left and right sides ofthe vehicle, and the pair of second ports are disposed at the otherright or left side of the vehicle. The fore-and-aft extended portion ofat least one of the pipes is extended along one of the left and rightside plates of the frame and connected to the second port. The at leastone of the pipes further includes a laterally extended portion which isextended in the lateral direction of the vehicle between the first portand the fore-and-aft extended portion of the at least one of the pipe. Astay is fixed on the first transaxle housing so as to support thelaterally extended portion of the at least one of the pipes.

Therefore, in the case that the pair of first ports and the pair ofsecond ports are opened laterally opposite to each other, the limitedspaces along the left and right side plates are used for piping of theaxle-driving pipes without interfering with another equipment, therebyminiaturizing the vehicle. Further, the stay prevents warp of thecorresponding pipe caused by the swing of the second transaxle aroundthe center pivot from being transmitted to the end of the pipe connectedto the corresponding first port, thereby preventing the pipe end and thefirst port from having oil leak and from being damaged.

Further preferably, the first transaxle housing includes a bossconnected to the frame, and wherein the stay is mounted onto the boss.Consequently, due to the support by the stay on the first transaxlehousing, the pipe end and the first port connected to each other arefurther surely prevented from moving relative to each other causing theoil leak and damage. The boss ordinarily formed on the first transaxlehousing serves as a fixture portion onto which the stay is fixed,thereby requiring no additional fixture member and saving costs.

Further preferably, the at least one of the pipes includes: a firstrigid pipe portion connected to one of the first ports and serving asthe laterally extended portion of the at least one of the pipes; asecond rigid pipe portion connected to one of the second ports; and aflexible pipe portion interposed between the first and second rigid pipeportions, wherein the flexible hose is extended along one of the leftand right side plates of the frame. Therefore, the flexible hose can bebent or curved so as to absorb stress on the pipe according to the swingof the second transaxle around the center pivot. Consequently, the atleast one pipe can be durable against the frequent swing of the secondtransaxle.

Alternatively, further preferably, the at least one of the pipesincludes: a rigid pipe portion connected to one of the first ports andextended along one of the left and right side plates of the frame so asto serve as the fore-and-aft extended portion; and a flexible pipeportion interposed between the rigid pipe portion and one of the secondports. Consequently, the main portion of the at least one pipe is therigid pipe portion whose internal pressure resistance is small so as toensure good fuel efficiency.

In either of the above two cases where the at least one pipe includesthe rigid pipe portion and the flexible pipe portion, the at least oneof the pipes further includes a swivel joint disposed between theflexible pipe portion and the first rigid pipe portion. The swivel jointabsorbs twist of the pipe caused by the swing of the second transaxlearound the center pivot, thereby inexpensively providing the pipe havinghigh durability against the swing of the second transaxle.

In the pipe arrangement when the pair of first ports and the pair ofsecond ports are laterally offset, preferably, the fore-and-aft extendedportions of both of the pipes are extended along one of the left andright side plates of the frame and connected to the respective secondports. Both of the pipes include the respective laterally extendedportions interposed between the respective first ports and therespective fore-and-aft extended portions thereof. The stay supports thelaterally extended portions of both of the pipes. Therefore, both of thefore-and-aft extended portions of the pipes are juxtaposed in thelimited space along the side plate so as to minimize the vehicle.Further, the stay prevents warp of both of the pipes caused by the swingof the second transaxle around the center pivot from being transmittedto the ends of the pipes connected to the respective first ports,thereby preventing the pipe ends and the first ports from having oilleak and from being damaged.

In the pipe arrangement when the pair of first ports and the pair ofsecond ports are laterally offset, alternatively, preferably, a firstpipe of the pipes is extended in the fore-and-aft direction of thevehicle from the corresponding first port along one of left and rightside plates of the frame, and a second pipe of the pipes includes thefore-and-aft extended portion extended along the other right or leftside plate and connected to the corresponding second port, and includesthe laterally extended portion connected to the corresponding first portand supported by the stay. Therefore, the fore-and-aft extended portionsof the pipes are disposed in the limited spaces along the respectiveleft and right side plates so as to minimize the vehicle. Further, thestay prevents warp of the second pipe caused by the swing of the secondtransaxle around the center pivot from being transmitted to the end ofthe second pipe connected to the first port, thereby preventing the endof the second pipe and the first port from having oil leak and frombeing damaged.

Further preferably, a stay is fixed onto the one of the left and rightside plates so as to support the first pipe. The stay on the side plateprevents warp of the first pipe, which is not supported by the stay onthe first transaxle housing, caused by the swing of the second transaxlearound the center pivot from being transmitted to the end of the firstpipe connected to the first port, thereby preventing the end of thefirst pipe and the first port from having oil leak and from beingdamaged.

In the vehicle according to the first aspect, preferably, the firsttransaxle housing is provided with a pair of outwardly opened thirdports, a hydraulic power steering valve is disposed on the frame betweenthe first and second transaxles, and a pair of power steering hydraulicpressure fluid pipes are interposed between the hydraulic power steeringvalve and the pair of third ports and extended along at least one of theaxle-driving hydraulic pressure fluid pipes. Therefore, the spacerequired for piping the pair of axle-driving hydraulic pressure fluidpipes and the pair of power steering hydraulic pressure fluid pipes andthe at least one axle-driving hydraulic pressure pipe is saved.

In the vehicle according to the first aspect, preferably, the pair offirst ports and the pair of third ports are disposed on the same sidesurface of the first transaxle housing. Consequently, the pair of powersteering hydraulic pressure fluid pipes and the at least oneaxle-driving hydraulic pressure fluid pipe are compactly collected inthe vicinity of the first transaxle so as to be connected to therespective third ports and the corresponding first port.

In the vehicle according to the first aspect, the first transaxlefurther includes a center section disposed in the first transaxlehousing and interposed between the hydraulic pump and the firsthydraulic motor. The center section is provided with a pair of first andsecond pump ports fluidly connected to the hydraulic pump, a pair offirst and second motor ports fluidly connected to the first hydraulicmotor, and a passage interposed between the first pump port and thefirst motor port. The pair of first ports are fluidly connected to thesecond pump port and the second motor port, respectively. Due to thecenter section, the component devices such as the hydraulic pump and thefirst hydraulic motor and the passage for connection of the hydraulicpump, the first hydraulic motor and the first ports are compactlyassembled together so as to minimize the first transaxle housing andexpand the space for piping.

Further preferably, the first transaxle further includes a charge pumpdisposed in the first transaxle housing so as to be driven together withthe hydraulic pump by the power from the prime mover through thetraveling power transmission system. One of the third ports is fluidlyconnected to the charge pump, and the other third port is fluidlyconnected to a fluid-suction side of the hydraulic pump. Due to thecharge pump, no additional device for supplying fluid to a hydraulicpower steering actuator is required so as to expand an area in thelimited space for piping the axle-driving and power steering hydraulicpressure fluid pipes, and save costs.

Further preferably, the first transaxle further includes a charge pumpcasing incorporating the charge pump. The charge pump casing is disposedin the first transaxle housing and connected to the center section. Thecharge pump casing is provided with a passage directly connected to thepair of third ports. Due to the charge pump casing, the charge pump andassociated equipments are compactly collected so as to minimize thefirst transaxle housing, thereby expanding the space for piping theaxle-driving and power steering hydraulic pressure fluid pipes.

Further preferably, the charge pump casing is provided with anotherpassage directly connected to the pair of first ports so as to fluidlyconnect the passage in the center section to the pair of first ports.Therefore, the inside portion of the charge pump casing is used forforming the passage directly connected to the first ports disposed onthe same side surface of the first transaxle housing with the thirdports, so as to reduce a space in the first transaxle housing for apassage interposed between the third ports and the first ports, i.e.,minimize the first transaxle housing, thereby expanding the space forpiping the axle-driving and power steering hydraulic pressure fluidpipes.

Further preferably, an adapter is attached onto the center section andprovided therein with a passage through which the pair of first portsare fluidly connected to the center section. Due to the easily removableadapter, the passage directly connected to the first ports disposed onthe same side surface of the first transaxle housing with the thirdports can be easily formed, and a space in the first transaxle housingfor a passage interposed between the third ports and the first ports isreduced, that is, the first transaxle housing is minimized, therebyexpanding the space for piping the axle-driving and power steeringhydraulic pressure fluid pipes.

A second object of the invention is to provide a hydraulic four-wheeldrive working vehicle equipped with a reservoir tank which prevents fueltherein from being contaminated with air so as to solve the aboveproblems.

To achieve the second object, in a second aspect of the invention, ahydraulically driven working vehicle comprises: a frame extended in thefore-and-aft direction of the vehicle; a first transaxle supported byone of front and rear portions of the frame, the first transaxleincluding a hydraulic pump, a first hydraulic motor fluidly connected tothe hydraulic pump, a first axle driven by the first hydraulic motor,and a first transaxle housing incorporating the hydraulic pump, thefirst hydraulic motor and the first axle, wherein the first transaxle isformed therein with a first fluid sump, and wherein the first transaxlehousing is provided with a pair of outwardly opened first ports fluidlyconnected to the hydraulic pump and the first hydraulic motor,respectively; a second transaxle supported by the other rear or frontportion of the frame, the second transaxle including a second hydraulicmotor fluidly connected to the hydraulic pump, a second axle driven bythe second hydraulic motor, and a second transaxle housing incorporatingthe second hydraulic motor and the second axle, wherein the secondtransaxle is formed therein with a second fluid sump, and wherein thesecond transaxle housing is provided with a pair of second ports fluidlyconnected to the second hydraulic motor; a pair of hydraulic pressurefluid pipes interposed between the pair of first ports and the pair ofsecond ports; a prime mover supported by the frame between the first andsecond transaxles; a traveling power transmission system supported bythe frame between the prime mover and the first transaxle so as todrivingly connect the hydraulic pump to the prime mover; a workingdevice disposed under the frame between the first and second transaxles;a working power transmission system supported by the frame between theprime mover and the working device so as to drivingly connect theworking device to the prime mover; and a reservoir tank fluidlyconnected to the hydraulic pump and the first and second hydraulicmotors. The reservoir tank is disposed so that a fluid level in thereservoir tank is higher than levels of the first and second fluidsumps. Therefore, fluid flowing from the reservoir tank to the first orsecond transaxle housing is prevented from being contaminated with air.

In the vehicle according to the second aspect, preferably, the reservoirtank is disposed just behind a rear end surface of the frame. Therefore,the reservoir tank exposed on the frame can be easily attached ordetached onto and from the frame, and easily subjected to maintenance.Further, the reservoir tank can be disposed behind rear wheel tires sothat the rear wheel tires do not hinder the attachment, detachment andmaintenance of the reservoir tank, and the damage of the reservoir tankby mud and stones stuck on the tire is reduced.

Alternatively, in the vehicle according to the second aspect,preferably, a breather provided on a top of the reservoir tank, whichalso serves as a fluid-supply opening of the reservoir tank, is disposedbehind a driver's seat of the vehicle. Therefore, the top of thebreather disposed outward of the vehicle facilitate fluid-supply to thereservoir tank.

In the vehicle according to the second aspect, preferably, a fuel tankis joined to the reservoir tank. Therefore, the number of requiredcomponent parts is reduced so as to facilitate assembling work of thevehicle.

Further preferably, a driver's seat is disposed above the firsttransaxle, so that the fuel tank and the reservoir tank are disposedbetween the seat and the first transaxle. Therefore, the space betweenthe first transaxle and the seat above the first transaxle iseffectively used for arranging the reservoir tank so as to reduce a deadspace, thereby minimizing the vehicle.

Further preferably, a breather provided on a top of the reservoir tank,which also serves as a fuel-support opening of the reservoir tank, isdisposed behind the seat. Therefore, fuel can be easily supplied to thereservoir tank.

Alternatively, in the vehicle according to the second aspect, thereservoir tank is disposed between a first wheel provided onto the firstaxle and a second wheel provided onto the second axle. This arrangementof the heavy reservoir tank improves the weight balance of the vehiclein the fore-and-aft direction.

Further preferably, a bonnet incorporating the prime mover alsoincorporates the reservoir tank. Therefore, the inner space of thebonnet is effectively used for arranging the reservoir tank so as tominimize the vehicle. Further, the cooling wind for the prime mover inthe bonnet can also cool the reservoir tank, thereby requiring noadditional device for cooling the reservoir tank.

Further preferably, a breather provided on a top of the reservoir tank,which also serves as a fluid-supply opening of the reservoir tank, isdisposed behind the seat. A dashboard of the vehicle is provided with anopening, which faces the top of the breather and is covered with aremovable lid. Due to such a simple structure, fuel can be easilysupplied through the dashboard into the reservoir tank.

A third object is to provide a hydraulic transaxle, which can serve as amain transaxle of a hydraulic four-wheel working vehicle, adapted toprevent pipes therearound from being complicated.

To achieve the third object, in a third aspect of the invention, atransaxle comprises: a transaxle housing supported by one of front andrear portions of a vehicle body frame; a hydraulic pump disposed in thetransaxle housing so as to be driven by power from a prime mover througha traveling power transmission system; a charge pump disposed in thetransaxle housing so as to be driven by the power from the prime moverthrough the traveling power transmission system; an axle disposed in thetransaxle housing so as to be driven by the hydraulic motor; a pair offirst ports provided on a side surface of the transaxle housing so as tobe fluidly connected to the hydraulic pump and the hydraulic motorrespectively; and a pair of second ports provided on the same sidesurface of the transaxle housing with the first ports. One of the secondports is fluidly connected to the charge pump, and the other second portis fluidly connected to a fluid-suction side of the hydraulic pump.

Therefore, hydraulic pressure fluid pipes for driving an auxiliarydevice (such as a power steering actuator) connected to the second portscan be compactly collected together with hydraulic pressure fluid pipesfor driving the axle of the first transaxle connected to the pair offirst ports. Further, due to the charge pump, the auxiliary device (suchas the power steering actuator) requires no additional fluid-supplydevice so as to save a space, i.e., to expand the space for the pipes,and to save the number of parts and costs.

In the transaxle according to the third aspect, preferably, a centersection is disposed in the transaxle housing and interposed between thehydraulic pump and the hydraulic motor. The center section is providedwith a pair of first and second pump ports fluidly connected to thehydraulic pump, a pair of first and second motor ports fluidly connectedto the hydraulic motor, and a passage interposed between the first pumpport and the first motor port. The pair of first ports are fluidlyconnected to the second pump port and the second motor port,respectively. Due to the center section, the component devices such asthe hydraulic pump and the first hydraulic motor and the passage forconnection of the hydraulic pump, the first hydraulic motor and thefirst ports are compactly assembled together so as to minimize thetransaxle housing and expand the space for pipes connected to the firstports and the second ports.

In the transaxle according to the third aspect, preferably, a chargepump casing incorporating the charge pump is disposed in the transaxlehousing and connected to the center section. The charge pump casing isprovided with a passage directly connected to the pair of second ports.Due to the charge pump casing, the charge pump and associated equipmentsare compactly collected so as to minimize the transaxle housing, therebyexpanding the space for pipes connected to the first ports and thesecond ports.

Further preferably, the charge pump casing is provided with anotherpassage directly connected to the pair of first ports so as to fluidlyconnect the passage in the center section to the pair of first ports.Therefore, the inside portion of the charge pump casing is used forforming the passage directly connected to the first ports disposed onthe same side surface of the transaxle housing with the second ports, soas to reduce a space in the transaxle housing for a passage interposedbetween the second ports and the first ports, i.e., minimize thetransaxle housing, thereby expanding the space for pipes connected tothe first ports and the second ports.

Alternatively, further preferably, an adapter is attached onto thecenter section and provided therein with a passage through which thepair of first ports are fluidly connected to the center section. Due tothe easily removable adapter, the passage directly connected to thefirst ports disposed on the same side surface of the transaxle housingwith the second ports can be easily formed, and a space in the transaxlehousing for a passage interposed between the second ports and the firstports is reduced, that is, the transaxle housing is minimized, therebyexpanding the space for pipes connected to the first ports and thesecond ports.

In the transaxle according to the third aspect, preferably, a pair ofthird ports is provided for fluidly connecting the pair of first portsto a second hydraulic motor for driving another axle. Due to thisarrangement, a vehicle equipped with the transaxle can be provided withcompactly collected hydraulic pressure fluid pipes, thereby beingminimized.

These, further and other objects, features and advantages will appearmore fully from the following description with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional side view of a hydraulic four-wheel drive workingvehicle according to a first embodiment of the invention.

FIG. 2 is a hydraulic circuit diagram of the hydraulic four-wheel driveworking vehicle according to the invention.

FIG. 3 is a sectional plan view of the hydraulic four-wheel driveworking vehicle according to the first embodiment, provided with anarrangement of hydraulic pressure fluid pipes.

FIG. 4 is a sectional view of a pipe stay support portion.

FIG. 5 is a sectional plan view of a rear transaxle provided on a leftside surface thereof with hydraulic fluid supply-and-delivery ports.

FIG. 6 is a sectional plan view of a rear transaxle provided on a rightside surface thereof with hydraulic fluid supply-and-delivery portsfacing forward.

FIG. 7 is a sectional plan view of a rear transaxle provided on a leftside surface thereof with hydraulic fluid supply-and-delivery portsfacing forward.

FIG. 8 is a rear view of a front transaxle.

FIG. 9 is a sectional plan view of the hydraulic four-wheel driveworking vehicle according to the first embodiment, provided with anotherarrangement of hydraulic pressure fluid pipes.

FIG. 10 is a sectional plan view of a hydraulic four-wheel drive workingvehicle according to a second embodiment of the invention, provided withan arrangement of hydraulic pressure fluid pipes.

FIG. 11 is a sectional plan view of the hydraulic four-wheel driveworking vehicle according to the second embodiment, provided withanother arrangement of hydraulic pressure fluid pipes.

FIG. 12 is a sectional plan view of a hydraulic four-wheel drive workingvehicle according to a third embodiment of the invention, provided withan arrangement of hydraulic pressure fluid pipes.

FIG. 13 is a sectional plan view of the hydraulic four-wheel driveworking vehicle according to the third embodiment, provided with anotherarrangement of hydraulic pressure fluid pipes.

FIG. 14 is a sectional side view of a hydraulic four-wheel drive workingvehicle according to a fourth embodiment of the invention, provided withan arrangement of a reservoir tank.

FIG. 15 is a sectional side view of a hydraulic four-wheel drive workingvehicle according to a fifth embodiment, provided with anotherarrangement of a reservoir tank.

FIG. 16 is a right side view of a rear transaxle for the vehicleaccording to the first embodiment.

FIG. 17 is a left side view of the rear transaxle according to the firstembodiment.

FIG. 18 is a sectional right side view of the rear transaxle accordingto the first embodiment, showing a center section and a charge pumpcasing in a transaxle housing.

FIG. 19 is a cross sectional view of the rear transaxle taken along anA-A line of FIG. 17.

FIG. 20 is a cross sectional view of the rear transaxle taken along aB-B line of FIG. 17.

FIG. 21 is a cross sectional view of the rear transaxle taken along aC-C line of FIG. 17.

FIG. 22 is a cross sectional view of the rear transaxle taken along aD-D line of FIG. 17.

FIG. 23 is a cross sectional view of the rear transaxle taken along anE-E line of FIG. 17.

FIG. 24( a) is a plan view of a bottom surface of the center sectionjoined to the charge pump casing, and FIG. 24( b) is a plan view of atop surface of the charge pump casing joined to the center section.

FIG. 25 is another hydraulic circuit diagram of a rear transaxleseparated from a pump housing.

FIG. 26 is a right side view of a rear transaxle according to a sixthembodiment.

FIG. 27 is a sectional plan view of the rear transaxle according to thesixth embodiment.

FIG. 28 is a sectional right side view of the rear transaxle accordingto the sixth embodiment, showing a center section and a charge pumpcasing in a transaxle housing.

FIG. 29 is a cross sectional view of the rear transaxle taken along anA-A line of FIG. 27.

FIG. 30 is a cross sectional view of the rear transaxle taken along aB-B line of FIG. 27.

FIG. 31( a) is a sectional plan view of the charge pump casing in therear transaxle according to the sixth embodiment, and FIG. 31( b) is asectional side view of the charge pump casing.

FIG. 32( a) is a plan view of a bottom surface of the center sectionjoined to the charge pump casing, and FIG. 32( b) is a plan view of atop surface of the charge pump casing joined to the center section,wherein the center section and the charge pump casing are provided forthe rear transaxle according to the sixth embodiment.

FIG. 33( a) is a sectional side view of a pipe connector fitted in atransaxle housing, and FIG. 33( b) is a sectional side view of anotherpipe connector fitted in a transaxle housing.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

Referring to FIGS. 1 to 3, a hydraulic four-wheel drive working vehicle100 according to a first embodiment of the invention will be described.Vehicle 100 is an Ackerman type steered lawn tractor, comprising: aframe 3; a rear transaxle 1; a front transaxle 2; an engine 10; atraveling power transmission system; a mower unit 20; and a mowerdriving power transmission system. Frame 3 includes parallel left andright side plates 3L and 3R extended in the fore-and-aft direction ofvehicle 100.

Rear transaxle 1 is supported by a rear portion of frame 3. Reartransaxle 1 includes a rear transaxle housing 1H, incorporating ahydraulic pump P, a hydraulic motor M1 (serving as a first hydraulicmotor) fluidly connected to hydraulic pump P, left and right rear wheelaxles 6 (serving as a first axle), and a deceleration gear train 37 anda differential gear unit 38 (see FIG. 2) interposed between hydraulicmotor M1 and axles 6. Rear transaxle housing 1H is outwardly opened by apair of traveling hydraulic fluid supply-and-delivery ports 1 a and 1 b,which are connected to hydraulic pump P and hydraulic motor M1,respectively.

Front transaxle 2 is supported by a front portion of frame 3. Fronttransaxle 2 includes a front transaxle housing 2H swingably supportedonto frame 3 through a center pivot 5. Front transaxle housing 2Hincorporates a pair of hydraulic motors M2 and M3, and left and rightfront wheel axles 8 driven by respective hydraulic motors M2 and M3.Front transaxle housing 2H is outwardly opened by a pair of travelinghydraulic fluid supply-and-delivery ports 2 a and 2 b, which are fluidlyconnected to respective hydraulic motors M2 and M3, so as to fluidlyconnect hydraulic motors M2 and M3 to hydraulic pump P in rear transaxle1.

Engine 10 is supported by frame 3 between rear and front transaxles 1and 2. The traveling power transmission system for drivingly connectinghydraulic pump P to engine 10 is supported by frame 3 between engine 10and rear transaxle 1.

Mower unit 20 is disposed under frame 3 between rear and fronttransaxles 1 and 2. The mower driving power transmission system fordrivingly connecting mower unit 20 to engine 10 is supported by frame 3between engine 10 and mower unit 20.

Vehicle 100 is provided with a pair of axle-driving hydraulic pressurefluid pipes 23 and 26 interposed between the pair of ports 1 a and 1 band the pair of ports 2 a and 2 b so as to fluidly connect hydraulicmotors M2 and M3 to hydraulic pump P. In this embodiment, ports 1 a and1 b of rear transaxle housing 1H are disposed rightward of vehicle 100,and ports 2 a and 2 b of front transaxle housing 2H are disposedleftward of vehicle 100. Pipes 23 and 26 are extended laterally (in theleft-and-right direction) from respective ports 1 a and 1 b, andextended in the fore-and-aft direction along an inside surface of leftside plate 3L of frame 3 in a gap between the inside surface of leftside plate 3L and the traveling power transmission system and themower-driving power transmission system, so as to be connected torespective ports 2 a and 2 b.

The laterally extended portions of pipes 23 and 26 are supported by aclamping stay 60 fixed on rear transaxle housing 1H. More specifically,rear transaxle housing 1H is formed with a boss to be attached to frame3, and clamping stay 60 is fixed onto the boss.

Pipes 23 and 26 b includes rigid pipes 23 b and 26 b connected to ports1 a and 1 b, and rigid pipes 23 c and 26 c connected to ports 2 a and 2b, respectively. Rigid pipes 23 b, 23 c, 26 b and 26 c are made ofmetal, for instance. Flexible hoses 23 a and 26 a are extended in thefore-and-aft direction along the inside surface of left side plate 3L soas to be interposed between rigid pipes 23 b and 23 c and between rigidpipes 26 b and 26 c, respectively. Flexible hoses 23 a and 23 b are madeof rubber withstanding pressure, for instance. Rigid pipes 23 b and 26 bserve as the laterally extended portions of pipes 23 and 26 connected tofirst ports 1 a and 1 b. Rigid pipes 23 b and 26 b are connected toflexible hoses 23 a and 26 a through swivel joints 54, respectively, andrigid pipes 23 c and 26 c to flexible hoses 23 a and 26 a through swiveljoints 55, respectively.

A hydraulic power steering valve 80 shown in FIG. 2 is disposed on frame3 between rear and front transaxles 1 and 2. Rear transaxle housing 1His rearwardly outwardly opened by auxiliary device driving hydraulicfluid supply-and-delivery ports 75 and 76. A pair of power steeringhydraulic pressure fluid pipes 81 and 82 are interposed between ports 75a and 76 and valve 80 along pipes 23 and 26.

In this embodiment, a reservoir tank 28 is disposed just behind a rearend surface of frame 3 so as to be fluidly connected to hydraulic pump Pand hydraulic motors M1, M2 and M3. Reservoir tank 28 is disposed sothat a fluid level in reservoir tank 28 is higher than fluid levels ofthe fuel sumps in respective transaxle housings 1H and 2H. Reservoirtank 28 is formed with an upright cylindrical fluid-supply portion 28 a.A breather 42, which also serves as a fluid-supply opening, is disposedon the top of fluid-supply portion 28 a behind a driver's seat.

Various sections in vehicle 100 will be more detailed. With respect tothe support of front transaxle 2 by the front portion of frame 3, asshown in FIGS. 1 to 3, a bracket 4 is fixed on the front portion offrame 3, and front transaxle housing 2H is swingably supported bybracket 4 through fore-and-aft horizontal center pivot 5, so that leftand right ends of front transaxle housing 2H are vertically swingable.

Left and right axles 6 are extended laterally outward from reartransaxle housing 1H, and fixed at distal ends thereof to centerportions of unsteerable rear wheels 7, respectively. Left and rightaxles 8 are extended laterally outward from front transaxle housing 2H,and drivingly connected at distal ends thereof to steerable front wheels9, respectively.

Engine 10 is vibro-isolatingly supported on an upper front portion offrame 3 through vibro-isolating rubbers or the like, and covered with abonnet. A steering wheel 12 is disposed upwardly rearward from the rearend of bonnet 11, and a speed control pedal 13 is disposed at a bottomportion of the rear end of bonnet 11. In seesaw-like shaped speedcontrol pedal 13, a front portion is depressed for controlling forwardtraveling speed of vehicle 100, and a rear portion is depressed forcontrolling backward traveling speed of vehicle 100. A speed controllever 14 pivoted on rear transaxle housing 1H interlocks with speedcontrol pedal 13. A brake pedal 41 is disposed in front of speed controlpedal 13. A rear cover 15 is mounted on an upper rear portion of frame3, and a driver's seat 16 is disposed on the top of rear cover 15.

Engine 10 is provided with a downward vertical output shaft 10 a. Apulley 10 b is fixed on output shaft 10 a, and a pulley 10 c is providedon a lower portion of output shaft 10 a below pulley 10 b through anelectromagnetic clutch 10 e. Rear transaxle 1 is provided with an inputshaft 17, which serves as a common pump shaft for hydraulic pump P and acharge pump 33, projecting upward from rear transaxle housing 1H. Apulley 17 a is fixed on input shaft 17. A belt is looped over pulleys 10b and 17 a so as to constitute the traveling power transmission systemfor drivingly connect hydraulic pump P in rear transaxle 1 to engine 10.A cooling fan 17 b is fixed on input shaft 17 so as to blow cooling windto rear transaxle housing 1H.

As shown in FIG. 3, twin tension pulleys 52 guide an intermediateportion of belt 18. Either of pulleys 52 has a pivot extended downwardfrom frame 3. A spring 53 for applying tension is hooked at one endthereof onto an arm supporting pulleys 52, and connected at the otherend thereof to frame 3.

As shown in FIG. 1, mower unit 20 incorporating rotary blades 20 a isvertically movably suspended under frame 3 between front wheels 9 andrear wheels 7. Mower unit 20 is provided at the top thereof with aninput pulley 20 b. A mower-driving belt (not shown) is looped overpulleys 10 c and 20 b so as to constitute the mower-driving powertransmission system for drivingly connecting rotary blades 20 a in mowerunit 20 to engine 10. Electromagnetic clutch 10 e interposed betweenpulley 10 c and engine output shaft 10 a is clutched on for transmittingpower of engine 10 to mower unit 20, and clutched off for isolatingmower unit 20 from the power of engine 10.

Rear transaxle housing 1H incorporates hydraulic pump P and hydraulicmotor M1 for driving rear wheels 7 (axles 6), front transaxle housing 2Hincorporates hydraulic motors M2 and M3 for driving respective frontwheels 9 (axles 8), and pipes 23 and 26 are interposed between transaxlehousings 1H and 2H, so as to constitute a hydrostatic transmission (HST)circuit HC1 including hydraulic pump P and hydraulic motors M1, M2 andM3.

HST circuit HC1 of vehicle 100 will be described with reference to FIG.2. As mentioned above, pipe 23 is interposed between port 1 a of reartransaxle housing 1H and port 2 a of front transaxle housing 2H, andpipe 26 is interposed between port 1 b of rear transaxle housing 1H andport 2 b of front transaxle housing 2H. In rear transaxle housing 1H, apassage 21 is interposed between hydraulic pump P and hydraulic motorM1, a passage 27 is interposed between hydraulic pump P and port 1 b,and a passage 22 is interposed between hydraulic motor M1 and port 1 a.

In rear transaxle housing 2H, fixed displacement hydraulic motor M2 andvariable displacement hydraulic motor M3 are connected to port 2 athrough a passage 24 in parallel, and connected to port 2 b through apassage 25 in parallel. Passage 24 is bifurcated into a passage 24 aconnected to hydraulic motor M2 and a passage 24 b to hydraulic motorM3, and passage 25 is bifurcated into a passage 25 a connected tohydraulic motor M2 and a passage 25 b connected to hydraulic motor M3.

In HST circuit having the above structure, hydraulic motor M1 of reartransaxle 1 and the pair of hydraulic motors M2 and M3 of fronttransaxle 2 are fluidly connected in series to hydraulic pump P.Hydraulic motors M2 and M3 in front transaxle 2 are fluidly connected inparallel with each other to hydraulic pump P so as to be differentiallydriven in correspondence to difference of load between left and rightfront wheels 9.

Regarding to circulation route in HST circuit HC1, when vehicle 100travels forward, fluid delivered from hydraulic pump P flows tohydraulic motors M2 and M3 through passage 27, port 1 b, pipe 26, port 2b and passage 25, and then flows to hydraulic motor M1 through passage25, port 2 a, pipe 23, port 1 a and passage 22, and returns to hydraulicpump P through passage 21. In other words, when vehicle travels forward,hydraulic pump P supplies fluid to hydraulic motors M2 and M3 of fronttransaxle 2 prior to hydraulic motor M1 of rear transaxle 1. Whenvehicle 100 travels backward, fluid flow delivered from hydraulic pumptakes a route opposite to the above route during forward traveling ofvehicle 100, so as to be supplied to hydraulic motor M1 of reartransaxle 1 prior to hydraulic motors M2 and M3 of front transaxle 2.

A drive mode switching valve (not shown) for setting vehicle 100 intoeither a two-wheel drive mode or a four-wheel drive mode may beinterposed between transaxles 1 and 2 across pipes 23 and 26. When thevalve is set at the four-wheel drive mode position, pipes 23 and 26 areentirely passed through the valve between ports 1 a and 2 a and between1 b and 2 b, respectively, thereby circulating fluid from hydraulic pumpP through hydraulic motor M1, M2 and M3. The valve when set at thetwo-wheel drive mode position makes a closed circuit between hydraulicpump P and hydraulic motor M isolated from ports 2 a and 2 b, so as tosupply fluid from hydraulic pump P to hydraulic motor M1, therebydriving rear wheels 7 (axles 6), and the valve also makes a closedcircuit between hydraulic motors M2 and M3 independent of the circuitbetween hydraulic pump P and hydraulic motor M1, so as to allowcirculation of fluid between hydraulic motors M2 and M3, therebyallowing free differential rotation of front wheels 9.

Transaxle housings 1H and 2H are filled with fluid so as to makerespective fluid sumps therein. Rear transaxle housing 1H is formed witha drain port 1 c connected to reservoir tank 28 through a drainpipe 29.Front transaxle housing 2H is formed with a drain port 2 c connected toreservoir tank 28 through a drainpipe 30. Therefore, reservoir tank 28absorbs fluid excessively expanded in the respective fluid sumps intransaxle housings 1H and 2H.

Charge pump 33 is disposed in rear transaxle housing 1H so as to supplyfluid to HST circuit HC1, and preferably driven by input shaft 17 whichalso serves as the pump shaft of hydraulic pump P. In rear transaxlehousing 1H, a suction line 31 is interposed between a fluid filter 32submerged in the fluid sump and charge pump 33 so as to supply fluid tocharge pump 33. Alternatively, charge pump 33 may suck fluid fromreservoir tank 28 disposed outside rear transaxle housing 1H.

A charge fluid passage 34 is extended from charge pump 33 and bifurcatesto be connected to passages 21 and 27 with hydraulic pump Ptherebetween. A pair of check valves 36 are disposed on the bifurcatingportions of charge fluid passage 34 connected to respective passages 21and 27. Due to this structure, fluid delivered from charge pump 33 isintroduced through corresponding check valve 36 into one of passages 21and 27 which is pressurized lower than the other passage 27 or 21.

A check valve 39 for preventing cavitation is connected in parallel withcharge pump 33 to suction line 31, and connected to charge fluid passage34 between charge check valves 35 through a later-discussed powersteering hydraulic fluid circuit. When one of pipes 21 and 27 ishydraulically depressed, check valve 39 introduces fluid from suctionline 31 to depressed passage 21 or 27 so as to assist the fluid supplyfrom charge pump 33.

In rear transaxle housing 1H, differential gear unit 38 differentiallyconnects axles 6 to each other, and deceleration gear train 37 isinterposed between a motor shaft of hydraulic motor M1 and differentialgear unit 38. Due to this structure, the output force of hydraulic motorM1 driven by hydraulic pump P is transmitted to rear wheels 7 on axles 6through deceleration gear train 37 and differential gear unit 38.Variable displacement hydraulic pump P is provided with a movable swashplate Pa interlocking with speed control lever 14 (see FIG. 1), which ispivoted on rear transaxle housing 1H and operatively connected to speedcontrol pedal 13. Due to the depression amount and direction of speedcontrol pedal 13, the tilt angle of swash plate Pa is controlled so asto determine the fluid delivery amount and direction from hydraulic pumpP, thereby determining the rotary speed and direction of rear wheels 7(and front wheels 9 in the four-wheel drive mode).

A manner of setting peripheral speeds of rear wheels 7 and front wheels9 according to the output rotation speed of hydraulic motor M1 andhydraulic motors M2 and M3, and a mechanism for setting the peripheralspeeds will now be described. In an ordinary manner, the peripheralspeeds of rear wheels 7 and front wheels 9 are set so that theperipheral speed of rear wheels 7 is equal to the peripheral speed offront wheels 9 when vehicle 100 travels straight. However, the strictequalization of peripheral speed between rear wheels 7 and front wheels9 causes frequent reverse of large and small peripheral speed relationbetween rear wheels 7 and front wheels 9 depending on the groundcondition. More specifically, during traveling of vehicle 100, the statethat the peripheral speed of rear wheels 7 exceeds the peripheral speedof front wheels 9 (i.e., front wheels 9 rotate following rear wheels 7,because front wheel or wheels 9 are loaded by the ground so that theperipheral speed of front wheels 9 becomes lower than the properperipheral speed thereof corresponding to the set output of hydraulicmotors M2 and M3) alternates with the state that the peripheral speed offront wheels 9 exceeds the peripheral speed of rear wheels 7 (i.e., rearwheels 7 rotate following front wheels 9, because rear wheel or wheels 7are loaded by the ground so that the peripheral speed of rear wheels 7becomes lower than the proper peripheral speed thereof corresponding tothe set output of hydraulic motor M1). Consequently, vehicle 100 travelsin uncomfortable stiff movement.

To solve the problem, in present vehicle 100, the output speeds ofhydraulic motor M1 and motors M2 and M3 are set so that the peripheralspeed of rear wheels 7 becomes slightly higher than the peripheral speedof front wheels 9 during straight traveling of vehicle 100. In otherwords, a front assist ratio (a degree of assisting the rotation of rearwheels 7 by the rotation of front wheels 9, i.e., a ratio of the setperipheral speed of front wheels 9 to the set peripheral speed of rearwheels 7) is set to be smaller than 1.0. Consequently, during straighttraveling of vehicle 100, front wheels 9 almost rotate following rearwheels 7. Even if rear wheel or wheels 7 are loaded and slowed down tosome degree so that the peripheral speed of rear wheels 7 becomes lowerthan the proper peripheral speed thereof corresponding to the set outputspeed of hydraulic motor M1, the peripheral speed of rear wheels 7 isstill higher than or equal to the peripheral speed of front wheels 9,i.e., the state that the rotation of rear wheels 7 assists the rotationof front wheels 9 is still maintained. In other words, during straighttraveling of vehicle 100 with hydraulic motors M1, M2 and M3 set as theabove, it rarely occurs that the peripheral speed of front wheels 9abnormally exceeds the peripheral speed of rear wheels 7. Therefore,vehicle 100 can comfortably travel without stiff movement.

However, due to the output rotary speed setting of hydraulic motors M1,M2 and M3 for making the peripheral speed of rear wheels 7 exceed theperipheral speed of front wheels 9, the rotation of front wheels 9follows the rotation of rear wheels 7 so as to cause a counter drivingforce from axles 8 to hydraulic motors M2 and M3, whereby hydraulicmotors M2 and M3 act as pumps so as to hydraulically depress the suctionports of motors M2 and M3, thereby causing cavitation in HST circuit HC1and causing hunting of vehicle 100. This phenomenon remarkably occurswhen vehicle 100 turns, especially sharply turns.

To solve the problem, a check valve is connected to a portion of HSTcircuit HC1, which serves as a suction part of hydraulic motors M2 andM3 (the series of passages 22, 23 and 24 (24 a and 24 b) betweenhydraulic motor M1 and the pair of hydraulic motors M2 and M3 duringforward traveling of vehicle 100, or the series of passages 21, 27, 26and 25 (25 a and 25 b) between hydraulic motor M1 and the pair ofhydraulic motors M2 and M3 through hydraulic pump P during backwardtraveling of vehicle 100), so as to supply fluid into HST circuit HC1from the outside of HST circuit HC1. In the embodiment of FIG. 2, acheck valve 40 is disposed in front transaxle 2 so as to introduce fluidfrom the fluid sump in front transaxle housing 2H into the suction partof hydraulic motors M2 and M3 during forward traveling of vehicle 100,and a check valve 39 is disposed in rear transaxle 1 so as to introducefluid from the fluid sump in rear transaxle housing 1H into the suctionpart of hydraulic motors M2 and M3 during backward traveling of vehicle100.

Incidentally, as mentioned above, during forward traveling of vehicle100, in vehicle 100, fluid is supplied to front hydraulic motors M2 andM3 prior to rear hydraulic motor M1. This fluid circulation route isadvantageous for forward descending a slope. When vehicle 100 travelsforward on a downhill, the weight of vehicle 100 applied on front wheels9 is larger than that applied on rear wheels 7, so that power requiredfor driving front wheels 9 is larger than that for driving rear wheels7. The fluid circulation route smoothens forward traveling of vehicle100 on a downhill.

However, when vehicle 100 travels forward on an uphill, the weight ofvehicle 100 applied on rear wheels 7 is larger than that applied onfront wheels 9, so that power required for driving rear wheels 7 islarger than that for driving front wheels 9. To correspond to this case,alternatively, the fluid circulation route may be reversed so as tosupply fluid to rear hydraulic motor M1 prior to front hydraulic motorsM2 and M3, thereby smoothening forward traveling of vehicle 100 on anuphill.

Vehicle 100 can be equipped with various working devices, such as afront blade, a front snowplow, a rear tiller and a plow, as well asmower unit 20. The diameter ratio between front tires and rear tiresvaries according to the weight and position of the working deviceequipped on vehicle 100. The variation of diameter ratio means variationof the front assist ratio. Vehicle 100 is provided on front transaxle 2with an adjustable cam mechanism CM for setting the front assist ratiointo a range between 0.7 and 1.0 in correspondence to the target workingdevice.

Cam mechanism CM will now be described with reference to FIG. 8 andothers. Cam mechanism CM is disposed on the rear portion of fronttransaxle 2. When steering wheel 12 is rotated from a neutral position(straight traveling position), a piston rod 90 of a power steeringcylinder 79 is telescoped through the later-discussed power steeringhydraulic circuit. The movement of piston rod 90 is transmitted to aleft front wheel support unit 48L so as to laterally turn left frontwheel 9 with left front wheel support unit 48L. The lateral turn of leftfront wheel 9 is transmitted to a right front wheel support unit 48Rthrough a tie rod 49 so as to laterally turn right front wheel 9 withright front wheel support unit 48R in the same direction with left frontwheel 9. The lateral turn of right front wheel support unit 48R istransmitted to cam mechanism CM through a control link 46. Cam mechanismCM comprises: a control lever 45 pivotally connected to control link 46through a pin 47; a control arm 43; and a swash plate pivot shaft M3 bserving as a rotary axis of a movable swash plate M3 a of hydraulicmotor M3. Cam mechanism CM converts the movement of control link 46 intorotational movement of swash plate pivot shaft M3 b so as to tilt swashplate M3 a at a target angle for reducing the displacement of hydraulicmotor M3, thereby accelerating front wheels 9 during turning of vehicle100.

Control arm 43 is fixed at one end thereof onto a portion of swash platepivot shaft M3 b projecting rearward from front transaxle housing 2H soas to be rotatable integrally with swash plate M3 a. Control arm 43 isprovided on the other end portion thereof with a contact plate 44abutting against control lever 45. Contact plate 44 is formed with twoslots through which respective adjusting bolts 44 a are screwed intocontrol arm 43. By loosening bolts 44 a, the position of contact plate44 can be adjusted so as to adjust the initial tilt angle of swash plateM3 a (during straight traveling of vehicle 100), i.e., adjust the frontassist ratio. As mentioned above, by this adjustment, the front assistratio is set within the range between 0.7 and 1.0 in correspondence tothe working device equipped onto vehicle 100.

Pin 47 is disposed behind front transaxle housing 2H, and the end ofcontrol link 46 is pivotally provided on pin 47 between the rear endsurface of front transaxle housing 2H and control lever 45, i.e., infront of control lever 45. A pivot shaft of control lever 45 coaxiallyengages to pin 47, thereby pivotally connecting control lever 45 tocontrol link 46. Due to this arrangement, control link 46 is disposedforward as far as possible, i.e., control link 46 extremely approachesthe rear surface of front transaxle 2H, so as to reduce the fore-and-aftwidth of front transaxle 2 with cam mechanism CM.

A hydraulic piping construction in vehicle 100 will be described. Tominimize a vehicle, hydraulic pressure fluid pipes are requested to becollected inside a vehicle frame. In working vehicle 100, fronttransaxle 2 incorporates left fixed displacement hydraulic motor M2 andright variable displacement hydraulic motor M3, as mentioned above.Therefore, cam mechanism CM for controlling swash plate M3 a ofhydraulic motor M3 is disposed eccentrically rightward on the rearportion of front transaxle 2, as shown in FIG. 8. Transaxle housing 2Hprojects rearward at the left portion thereof laterally opposite to cammechanism CM so as to have the pair of leftwardly opened ports 2 a and 2b.

On the other hand, rightwardly opened ports 1 a and 1 b of reartransaxle 1 are disposed at the right side surface of rear transaxlehousing 1H. This arrangement of ports 1 a and 1 b and ports 2 a and 2 brequires pipes 23 and 26 to be disposed rightward from ports 1 a and 1 bat the right rear portion of vehicle 100, and to be disposed leftward ofthe front portion of vehicle 100 so as to be connected to ports 2 a and2 b. However, the traveling power transmission system and themower-driving power transmission system occupy a main space inside frame3. Further, mower unit 20 is disposed under the middle portion of frame3. Consequently, the space for arranging pipes 23 and 26 between thefront and rear portions of vehicle 100 without interfering with thepower transmission systems and mower unit 20 is limited.

Other required things in arrangement of pipes are that the piping workrequires no other device to be removed, and that work for attachinganother device requires no pipe to be removed. Further, to reduceinternal pressure resistance in pipes, the pipes include few bentportions as much as possible, and rigid pipes such as steel pipes aredesired to serve as the hydraulic pressure fluid pipes. On the otherhand, prevention of excessive twist and folding of the pipes caused bythe swing of front transaxle 2 around center pivot 5, and prevention ofends of pipes connected to ports from having fluid leak and from beingdamaged are requested.

Arrangement of pipes in vehicle 100 solving these problems will bedescribed. In this regard, referring to FIGS. 1 and 3, extension routesof pipes 23 and 26 from ports 1 a and 1 b on rear transaxle housing 1Hwill be described. Rear rigid pipes 23 b and 26 b of pipes 23 and 26 areextended rightward from ports 1 a and 1 b, bent, extended upwardlyforward, bent again, and extended leftward just in front of the frontend surface of rear transaxle housing 1H. Clamping stay 60 fixed onhousing 1H clamps the laterally (leftward) extended intermediateportions of rear rigid pipes 23 b and 26 b. As shown in FIG. 4( a),clamping stay 60 is fixed on a mount boss 70 formed on housing 1H. Mountboss 70 is used for attaching rear transaxle 1 onto a frame of anothertype vehicle. Arrangement of clamping stay 60 will be detailed later.

Rear rigid pipes 23 b and 26 b extended leftward just in front of reartransaxle housing 1H are bent at the left portions thereof, extendedvertically upward, bent again, and extended horizontally forward alongthe bottom edge of left side plate 3L when viewed in side as shown inFIG. 1, and along the inside surface of left side plate 3L when viewedin plan as shown in FIG. 3. A clamping stay 61 is fixed onto left sideplate 3L so as to clamp the horizontally forward extended portions ofrear rigid pipes 23 b and 26 b.

Rear rigid pipes 23 b and 26 b are swivellably connected to respectiverear ends of flexible hoses 23 a and 26 a through respective swiveljoints 54 in front of clamping stay 61. Flexible hoses 23 a and 26 a areextended substantially horizontally forward, i.e., substantiallycoaxially to rear rigid pipes 23 b and 26 b, along the bottom edge ofleft side plate 3L when viewed in side as shown in FIG. 1, and along theinside surface of left side plate 3L when viewed in plan as shown inFIG. 3. Flexible hoses 23 a and 26 a are connected at front ends thereofto respective rear ends of front rigid pipes 23 c and 26 c throughrespective swivel joints 55 adjacent to a front portion of left sideplate 3L. Front rigid pipes 23 c and 26 c are extended horizontallyforward from respective swivel joints 55, bent and extended leftwardlydownward just behind front transaxle 2 so as to be connected torespective ports 2 a and 2 b on front transaxle housing 2H.

Due to this arrangement, the whole pipes 23 and 26 between ports 1 a and1 b and ports 2 a and 2 b are prevented from interfering with anotherdevice or member. In this regard, the fore-and-aft extended mainportions of pipes 23 and 26 (including flexible hoses 23 a and 26 a) aredisposed along the bottom edge of left side plate 3L when viewed inside, higher than mower unit 20, thereby being prevented frominterfering with mower unit 20. Also, the fore-and-aft extended mainportions of pipes 23 and 26 (including flexible hoses 23 a and 26 a) aredisposed along the inside surface of left side plate 3L when viewed inplan, leftward from the traveling power transmission system, includingpulley 10 b and belt 18, the mower-driving power transmission system,including pulley 20 b and the mower-driving belt, and the operation linkmechanisms interlocking with speed control pedal 13 and brake pedal 41.

Rigid pipes 23 b, 23 c, 26 b and 26 b can be diametrically large so asto reduce the internal pressure resistance therein. Further, all thebent portions of pipes 23 and 26 are provided on rigid portions rigidpipes 23 b, 23 c, 26 b and 26 b, and the number of bent portions arereduced as much as possible. Flexible hoses 23 a and 26 a are disposedalong left side plate 3L so as to absorb the deflection of pipes 23 and26 caused by the swing of front transaxle 2 around center pivot 5.Consequently, pipes 23 and 26 are prevented from being unexpectedly bentor being broken at ends thereof connected to ports 1 a, 1 b, 2 a and 2b.

Due to the clamping of rear rigid pipes 23 b and 26 b by clamping stays60 and 61, ends of rigid pipes 23 b and 26 b connected to ports 1 a and1 b are prevented from receiving excessive bending force, shearingforce, and stretching force, and thereby being prevented from havingfluid leak or being damaged. Further, swivel joints 54 and 55 absorbtwist of pipes 23 and 26 caused by the swing of front transaxle 2 aroundcenter pivot 5 so as to prevent pipes 23 and 26 from being damaged ordeformed caused by the twist.

The power steering hydraulic circuit system and associate piping invehicle 100 will be described with reference to FIG. 2. In vehicle 100,power steering cylinder 79 is supplied with fluid from charge pump 33.The pair of auxiliary device driving hydraulic fluid supply-and-deliveryports 75 and 76 are disposed on rear transaxle housing 1H. In reartransaxle housing 1H, charge pump 33 is connected through a passage 98to port 75, and through a passage 99 to port 76. Hydraulic powersteering valve 80 is provided with a pair of ports 85 and 86corresponding to respective ports 75 and 76. At the outside of reartransaxle housing 1H, pipe 81 is interposed between ports 75 and 85, andpipe 82 is interposed between ports 76 and 86. Hydraulic power steeringvalve 80 is also provided with a pair of ports 87 and 88 correspondingto front and rear ports of power steering cylinder 79. A hydraulicpressure fluid pipe 83 is interposed between port 87 and the front portof power steering cylinder 79, and a hydraulic pressure fluid pipe 84 isinterposed between port 88 and the rear port of power steering cylinder79.

In the above hydraulic circuit system, valve 80 is switchedcorrespondence to the rotation angle and direction of steering wheel 12,so as to control fluid-supply from charge pump 33 to power steeringcylinder 79.

A relief valve 50 is interposed between pipes 98 and 99. Whenhigher-pressurized pipe 98 is excessively pressurized, relief valve 50is opened so as to bypass excessive pressure fluid fromhigher-pressurized pipe 98 to lower-pressurized pipe 99 so as toregulate the hydraulic pressure in the power steering hydraulic circuitsystem. In rear transaxle housing 1H, the recovery fluid flowing in pipe82 joins the excessive pressure fluid released from relief valve 50 soas to be charged to HST circuit HC1.

Referring to arrangement of power steering hydraulic pressure fluidpipes 81 and 82, as shown in FIG. 1, ports 75 and 76 are juxtaposedbehind ports 1 a and 1 b on the right side surface of rear transaxlehousing 1H. Pipes 81 and 82 are extended from respective ports 75 and 76along pipes 23 and 26, as partly shown in FIGS. 1 and 3, i.e., in acourse similar to the course of pipes 23 and 26, so that the forwardlyextended main portions of pipes 75 and 76 are extended along the insidesurface of left side plate 3L when viewed in plan. Pipes 75 and 76 arebent at front ends of the forwardly extended portions thereof behindvalve 80, extended upward, bent again and extended rightward above belt18 so as to be connected to ports 85 and 86 of valve 80.

In this way, the portions of pipes 81 and 82 from the rear ends thereofconnected to ports 75 and 76 to the front ends of the forwardly extendedportions thereof are disposed along pipes 23 and 26 prevented frominterfering with the traveling power transmission system, themower-driving power transmission system and mower unit 20. Further, allthe fore-and-aft extended main portions of pipes 23 and 26 and pipes 81and 82 are compactly collected along left side plate 3L.

As shown in FIG. 3, power steering cylinder 79 is fixed onto frame 3 soas to be disposed along the outside surface of left side plate 3L.Piston rod 90 of power steering cylinder 79 is pivotally connected atthe front end thereof to a bracket 48 a extended from the top of leftfront wheel support unit 48L, so as to be prevented from interferingwith cam mechanism CM disposed rightward on rear transaxle 2 andconnected to right front wheel support unit 48R. Piston rod 90 istelescoped according to operating steering wheel 12, so as to leftwardlyor rightwardly turn left and right front wheels 9 together with left andright front wheel support units 48L and 48R.

Clamping stays 60 and 61 for clamping pipes 23 and 26 will be describedwith reference to FIGS. 4( a) and 4(b). Referring to FIG. 4( a),clamping stay 60 comprises a main stay member 66 and a keep plate 67.Main stay member 66 includes a tab portion fastened to mount boss 70 ofrear transaxle housing 1H through a bolt 71. Main stay member 66 alsoincludes a pipe support portion for supporting rear rigid pipes 23 b and26 b of pipes 23 and 26. The pipe support portion is formed with a pairof sectionally semicircular grooves into which rear rigid pipes 23 b and26 b are fitted. Keep plate portion 67 is fastened to the pipe supportportion of main stay member 66 through bolts 72, whereby rear rigidpipes 23 b and 26 b are clamped between main stay member 66 and keepplate portion 67. Incidentally, a shock absorbing rubber 66 a is fittedbetween stay member 66 and keep plate portion 67 so as to be woundaround pipe portions 23 b and 26 b, thereby preventing noise from a gapbetween rigid pipes 23 b and 26 b and clamping stay 60.

In this way, clamping stay 60 is fixed on rear transaxle housing 1H soas to clamp the laterally extended portions of rigid pipes 23 b and 26b. In the embodiment shown in FIGS. 1 and 4( a), clamping stay 60 isdisposed so as to vertically align the laterally extended portions ofrigid pipes 23 b and 26 b. Alternatively, clamping stay 60 may bedisposed onto rear transaxle housing 1H so as to horizontally align thelaterally extended portions of rigid pipes 23 b and 26 b.

Referring to FIG. 4( b), clamping stay 61 comprises a main stay member68 and a keep plate 69. Main stay member 68 includes a tab portionfastened to frame 3, more specifically, side plate 3L or 3R (in thisembodiment, left side plate 3L), through a bolt 73. Main stay member 68also includes a pipe support portion for supporting rear rigid pipes 23b and 26 b of pipes 23 and 26. The pipe support portion is formed with apair of sectionally semicircular grooves into which rear rigid pipes 23b and 26 b are fitted. Keep plate portion 69 is fastened to the pipesupport portion of main stay member 68 through bolts 74, whereby rearrigid pipes 23 b and 26 b are clamped between main stay member 68 andkeep plate portion 69. Incidentally, a shock absorbing rubber 68 a isfitted between stay member 68 and keep plate portion 69 so as to bewound around pipe portions 23 b and 26 b, thereby preventing noise froma gap between rigid pipes 23 b and 26 b and clamping stay 61.

In this way, clamping stay 61 is fixed onto left side plate reartransaxle housing 1H so as to clamp the fore-and-aft extended portionsof rigid pipes 23 b and 26 b. In the embodiment shown in FIGS. 1 and 4(b), clamping stay 61 is disposed so as to vertically align thefore-and-aft extended portions of rigid pipes 23 b and 26 b.Alternatively, clamping stay 61 may be disposed onto rear transaxlehousing 1H so as to horizontally align the fore-and-aft extendedportions of rigid pipes 23 b and 26 b.

The above-mentioned arrangement of pipes 23 and 26 is associated withthe rightwardly outward opened ports 1 a and 1 b on the right side ofrear transaxle 1. Alternatively, referring to FIG. 5, ports 1 a and 1 bare opened leftwardly outward on the left side of rear transaxle 1,i.e., on the same lateral side of vehicle 100 with ports 2 a and 2 b offront transaxle 2. In this regard, rear rigid pipes 23 b and 26 b arebent upwardly forward from rear ends thereof connected to ports 1 a and1 b of rear transaxle 1, and bent again so as to be extendedhorizontally forward along left side plate 3L (along the bottom edge ofleft side plate 3L when viewed in side, and along the inside surface ofleft side plate 3L when viewed in plan). The arrangement of pipes 23 and26 between swivel joints 54 and ports 2 a and 2 b is similar to thearrangement when ports 1 a and 1 b are disposed on the right side ofrear transaxle 1.

Further alternatively, referring to FIG. 6, a port block PB is fixedonto the right side surface of rear transaxle housing 1H. Port block PBis bored with L-like shaped end portions of passages 22, 27, 98 and 99(see FIG. 2). Ports 1 a and 1 b at front ends of respective passages 22and 27, and ports 75 and 76 at front ends of respective passages 98 and99 are forwardly outward opened on the front end surface of port blockPB. The space within port block PB required for rightward-to-forwardcourse change of passages 22, 27, 98 and 99 is smaller than the spacerequired for rightward-to-forward course change of external pipes 23 (23b), 26 (26 b), 81 and 82, i.e., for curving or bending the externalpipes. Therefore, port block PB provided with ports 1 a, 1 b, 75 and 76on the front end surface thereof is available for arranging pipes 23 and26 (and 81 and 82) inside frame 3 in vehicle 100 having a very narrowgap between rear transaxle housing 1H and right side plate 3R of frame3, because, if pipes 23 and 26 are connected to ports 1 a and 1 bwithout port block PB in the condition that the gap between reartransaxle housing 1H and right side plate 3R is very narrow, pipes 23and 26 extended rightward from ports 1 a and 1 b cannot be curvedforward within the very narrow gap between rear transaxle housing 1H andright side plate 3R (i.e., pipes 23 b and 26 b cannot help projectingrightward from right side plate 3R of frame 3 to be curved forward).

Alternatively, referring to FIG. 7, port block PB bored with L-likeshaped end portions of passages 22, 27, 98 and 99 is fixed onto the leftside surface of rear transaxle housing 1H, so as to provide forwardlyoutward opened ports 1 a, 1 b, 75 and 76 at the left side of reartransaxle 1. Incidentally, the structure in the front portion of vehicle100 which is omitted in each of FIGS. 5 to 7 is the same as that shownin FIGS. 1 and 3.

Arrangement of reservoir tank 28 in vehicle 100 will be described. Invehicle 100 shown in FIGS. 1 and 3 (also in the cases of FIGS. 5, 6 and7), reservoir tank 28 is disposed just behind the rear end surface offrame 3, and disposed in rear cover 15, so that the fluid level inreservoir tank 28 is higher than the fluid levels of the respectivefluid sumps in front and rear transaxle housings 1H and 2H. Reservoirtank 28 is fluidly connected to front and rear transaxles 1 and 2through respective drain pipes 29 and 30 so as to absorb excessive fluidfrom front and rear transaxle housings 1H and 2H.

The arrangement of reservoir tank 28 behind the rear end surface offrame 3 is available for works of attachment, detachment and maintenanceof reservoir tank 28, because reservoir tank 28 disposed at thisposition comes behind tires of rear wheels 7, and does not require rearwheels 7 to be detached for the works. During traveling of vehicle 100,the defect of reservoir tank 28 yielded to stones or mud spattered orknocked by the tires of rear wheel 7 becomes fewer.

Reservoir tank 28 is disposed upright (vertically long) so as toheighten the fluid level therein. Even if vehicle 100 travels on aslope, the high fluid level in reservoir tank 28 prevents the fluid sumpin front and rear transaxle housings 1H and 2H from being contaminatedwith air bubbles, thereby preventing fluid circulating among hydraulicpump P and hydraulic motors M1, M2 and M3 from being contaminated withair bubbles. The vertical length of upright reservoir tank 28 issufficient to prevent the fluid level surface from touching the bottomsurface of reservoir tank 28 regardless of the swing of front transaxle2 around center pivot 5.

Another advantage of reservoir tank 28 disposed behind the rear endsurface of frame 3 is to provide a sufficient length of drainpipe 30between front transaxle 2 and reservoir tank 28 so as to correspond tothe swing of front transaxle 2 around center pivot 5.

Rear cover 15 is provided at a top portion thereof behind driver's seat16 with a hole, through which upright cylindrical fluid-supply portion28 a of reservoir tank 28 projects upwardly outward. Breather 42,serving as the fluid-supply opening of reservoir tank 28, is disposed onthe top of fluid-supply portion 28 a above the top of rear cover 15,thereby facilitate fuel-supply work by a driver on seat 16. Further, dueto such a high position of breather 42 (i.e., the fluid-supply openingof reservoir tank 28), fuel is prevented from overflowing from breather42 even when vehicle 100 travels on a slope.

Alternatively, referring to FIG. 9, pipes 23 and 26 comprise flexiblehoses (such as pressure rubber hoses) 23 d and 26 d and rigid pipes(such as metal or steel pipes) 23 e and 26 e. Flexible hoses 23 d and 26d are connected to respective ports 2 a and 2 b of front transaxle 2.Rigid pipes 23 e and 26 e include the fore-and-aft main portion of pipes23 and 26 and are connected to ports 1 a and 1 b of rear transaxle 1.

Rigid pipes 23 e and 26 e include the same arrangement of rigid pipes 23b and 26 b. In this regard, rigid pipes 23 e and 26 e connected to ports1 a and 1 b includes laterally extended portions, which are disposedjust in front of rear transaxle housing 1H and clamped by clamping stay60 fixed on mount boss 70 of rear transaxle housing 1H. The fore-and-aftextended main portions of rigid pipes 23 e and 26 e are extended alongleft side plate 3L (along the bottom edge of left side plate 3L whenviewed in side, and along the inside surface of left side plate 3L whenviewed in plan), so as to replace the fore-and-aft extended frontportions of rigid pipes 23 b and 26 b and flexible hoses 23 a and 26 a.Rigid pipes 23 e and 26 e are connected at front ends thereof torespective flexible hoses 26 d and 26 e through respective swivel joints55. The fore-and-aft extended main portions of rigid pipes 23 e and 26 eare clamped by a clamping stay 63 fixed onto left side plate 3L justbehind swivel joints 55.

Vehicle 100 shown in FIG. 9 may be provided with any of otherarrangements of ports 1 a and 1 b on rear transaxle 1 shown in FIGS. 5,6 and 7. In this case, rigid pipes 23 e and 26 e are rearranged to suitthe arrangement of ports 1 a and 1 b.

Flexible hoses 23 d and 26 d are extended forward from swivel joints 55and bent rightwardly downward just behind of rear transaxle 2 so as tobe connected to ports 2 a and 2 b on the rear end of rear transaxlehousing 2H.

The arrangement of pipes 23 and 26 shown in FIG. 9 has the sameadvantages with the arrangement of pipes 23 and 26 shown in FIGS. 1 and3, and additionally, has an advantage in reduction of flexible pipeportions, which are diametrically smaller than rigid pipe portions andhave large internal pressure resistance. Namely, the reduction offlexible pipe portions leads to reduction of internal pressureresistance in pipes 23 and 26.

Referring to FIG. 1, a pair of left and right mower hangers 91 aredisposed in front of front transaxle 2. Mower hangers 91 are extendeddownward from bottoms of respective side plates 3L and 3R just in frontof front transaxle 2, and bent to be extended rearwardly downward underfront transaxle 2. Left and right link rods 91 a are pivotally connectedat front ends thereof onto rear ends of respective mower hangers 91, andextended rearwardly downward so as to be pivotally connected at rearends thereof to respective front hooks of mower unit 20. Therefore,mower unit 20 can be tilted in the fore-and-aft direction relative tovehicle 100, so as to fit the ground during traveling of vehicle 100.

To ensure a proper performance of link rods 91 a serving as a parallellinkage, location of mower hangers 91 is important. Conventional mowerhangers disposed behind front transaxle 2 are troublesome to be attachedor detached to and from frame 3 or to be reformed. In the presentvehicle 100, mower hangers 91 disposed in front of front transaxle 2 canbe easily and efficiently attached to frame 3 while adjusting itsvertical and fore-and-aft position. Further, due to the arrangement ofmower hangers 91 in front of front transaxle 2, front transaxle 2 isshifted rearward from its conventional position so as to shorten the gapbetween rear wheel axles 6 and front wheel axles 8, thereby reducing theturning radius of vehicle 100.

Incidentally, engine 10 is provided with a muffler 10 d disposed on afront end portion of frame 3 in front of front transaxle 2. Frame 3 isintegrally formed with a muffler cover 3 a covering a front surface ofmuffler 10 d. Muffler cover 3 a serves as a part of a bumper of vehicle100.

Structure of rear transaxle 1 will be described with reference to FIGS.16 to 24. As shown in FIG. 16, main ports 1 a and 1 b and auxiliaryports 75 and 76 are juxtaposed on the same (right) side surface ofhousing 1H, thereby compactly collecting axle-driving hydraulic pressurefluid pipes 23 and 26 and power steering hydraulic pressure fluid pipes81 and 82 so as to be connected to these ports.

As mentioned above, in rear transaxle housing 1H are disposed hydraulicpump P and charge pump 33, which are driven by power from engine 10through the traveling power transmission system disposed out of reartransaxle 1, hydraulic motor M1 fluidly connected to hydraulic pump P,and axles 6 driven by hydraulic motor M1. Also, in rear transaxlehousing 1H are disposed passage 21 interposed between hydraulic pump Pand port 1 a, passage 27 interposed between hydraulic motor M1 and port1 b, passage 98 interposed between charge pump 33 and port 75, andpassage 99 interposed (through either of charge check valves 35) betweenthe suction (lower-pressurized) side of hydraulic pump P (i.e., eitherof passages 21 and 27) and port 76 (see FIG. 2).

Further, in rear transaxle housing 1H is disposed a center section 101interposed between hydraulic pump P and hydraulic motor M1. Centersection 101 is formed with a pair of pump kidney ports 57 a and 57 bopened to hydraulic pump P, and with a pair of motor kidney ports 56 aand 56 b opened to hydraulic motor M1. Passage 21 fluidly connectinghydraulic pump P and hydraulic motor M1 to each other is bored withincenter section 101 so as to be interposed between kidney ports 57 a and56 a. A part of passage 22 interposed between hydraulic pump P and port1 a is bored within center section 101 so as to be connected to kidneyport 57 b. A part of passage 27 interposed between hydraulic motor M1and port 1 b is bored within center section 101 so as to be connected tokidney port 56 b.

In rear transaxle housing 1H is also disposed a charge pump casing 102joined to center section 101. Charge pump casing 102 incorporates chargepump 33 and is formed therein with a part of passage 98 to be connectedto port 75, and a part of passage 99 to be connected port 76. Chargepump casing 102 is also formed therein with a part of passage 22interposed between hydraulic pump P and port 1 a, and a part of passage27 interposed between hydraulic motor M1 and port 1 b. The parts ofpassages 22 and 27 within charge pump casing 102 continue to therespective parts of passages 22 and 27 within center section 101 so asto be connected to respective kidney ports 57 b and 56 b.

Referring to FIG. 17, the inner space of rear transaxle housing 1H ispartitioned by a partition wall between a hydraulic circuit chamber anda transmission gear chamber. Hydraulic pump P and motor M1 are disposedin the hydraulic circuit chamber, and deceleration gear train 37,differential gear unit 38 and axles 6 are disposed in the transmissiongear chamber. As shown in FIGS. 16 and 23, rear transaxle housing 1H isconstituted by upper and lower halves joined to each other through bolts153.

Referring to FIG. 21, as mentioned above, the upper portion of inputshaft 17 projecting vertically upward from rear transaxle housing 1H isfixedly provided thereon with input pulley 17 a so as to be drivinglyconnected to engine 10 through belt 18, and is fixedly provided thereonwith cooling fan 17 b for cooling rear transaxle housing 1H under pulley17 a. In rear transaxle housing 1H, vertical input pulley 17 serves asthe rotary axial shaft of hydraulic pump P.

Variable displacement hydraulic pump P, having input shaft 17 serving asthe vertical rotary axis thereof, is vertically mounted onto a rear topsurface of center section 101 at which kidney ports 57 a and 57 b areopened. Fixed displacement hydraulic motor M1, having a laterally(leftward) horizontal motor shaft 127 serving as the rotary axisthereof, is mounted onto a front left side surface of center section 101at which kidney ports 56 a and 56 b are opened, so as to be fluidlyconnected to hydraulic pump P. Motor shaft 127 is drivingly connected todeceleration gear train 37 so as to transmit the output force ofhydraulic motor M1 to axles 6 through deceleration gear train 37 anddifferential gear unit 38.

As shown in FIG. 23, vertical input shaft 17 penetrates center section101 and is inserted into charge pump casing 102 attached to the bottomsurface of center section 101 so as to serve as the drive shaft ofcharge pump 33 in charge pump casing 102. Charge pump 33 sucks fluidfrom the fluid sump in rear transaxle housing 1H so as to supply fluidto the axle-driving hydraulic circuit, and to the auxiliary device(power steering) driving hydraulic circuit through ports 75 and 76.

As shown in FIGS. 16 and 21, speed control lever 14 operativelyconnected to speed control pedal 13 is pivoted on rear transaxle housing1H so as to control the tilt angle and direction of swash plate Pa ofhydraulic pump P.

The structure of the hydraulic circuit system in rear transaxle 1 willbe more detailed. As shown in FIGS. 17 and 24( b), center section 101 isfastened to an inside wall of rear transaxle housing 1H through bolts151. As shown in FIG. 17, the circular rear top surface of centersection 101, onto which hydraulic pump P is mounted, serves as a pumpcontact surface 103. In pump contact surface 103, right pump kidney port57 a and left pump kidney port 57 b are laterally symmetrically openedupward, and a vertical shaft hole 17 n, into which input shaft 17 isrotatably inserted, is opened upward between right and left pump kidneyports 57 a and 57 b. Vertical shaft hole 17 n is passed through centersection 101 and also opened downward at the bottom surface of centersection 101.

As shown in FIG. 21, a cylinder block 104 of hydraulic pump P isslidably rotatably fitted onto pump contact surface 103 so as to opencylinder holes therein to pump kidney ports 57 a and 57 b, and isnot-relatively rotatably fitted on input shaft 17 passed through shafthole 17 n (in a spline-engaging manner). Pistons 109 are reciprocallyslidably fitted in the respective cylinder holes of cylinder block 104,and project at heads thereof outward from cylinder block 104 so as toabut against movable swash plate Pa. Input shaft 17 projects upward fromcylinder block 104, freely penetrates movable swash plate Pa, andprojects upward from the top wall of rear transaxle housing 1H so as tobe fixedly provided thereon with pulley 17 a and cooling fan 17 b, asmentioned above. Input shaft 17 inserted in shaft hole 17 n alsoprojects downward from center section 101 into charge pump casing 102 soas to serve as the drive shaft of charge pump 33.

Referring to FIGS. 17, 18 and 20, a fore-and-aft horizontal passage hole21, serving as passage 21 interposed between hydraulic pump P and motorM1, is bored in center section 101, so as to be connected at a rearupper end portion to right pump kidney ports 57 a, and at a front upperend portion thereof to rear motor kidney port 56 a. The part of passage27 bored in center section 101 comprises fluid passage holes 27 c, 27 dand 27 e, and the part of passage 27 bored in charge pump casing 102 isa fluid passage hole 27 b. Fluid passage hole 27 e is extendedrightwardly downward from left pump kidney port 27 b to a fore-and-aftintermediate portion of fluid passage hole 27 d. Fluid passage hole 27 dis fore-and-aft horizontally extended under fluid passage hole 21 inparallel, and connected at a front end portion thereof to vertical fluidpassage hole 27 c. Fluid passage hole 27 c is opened downward at thebottom surface of center section 101 so as to be directly coaxiallyconnected to vertical fluid passage hole 27 b bored in charge pumpcasing 102.

As shown in FIG. 23, the circular front left side surface of centersection 101, onto which hydraulic motor M1 is mounted, serves as a motorcontact surface 129. In motor contact surface 129, rear motor kidneyport 56 a and front motor kidney port 56 b are symmetrically openedleftward, and a lateral horizontal shaft hole 127 a, into which motorshaft 127 is rotatably inserted, is opened leftward between rear andfront motor kidney ports 56 a and 56 b.

As shown in FIG. 17, a cylinder block 120 of hydraulic motor M1 isslidably rotatably fitted onto motor contact surface 129 so as to opencylinder holes therein to motor kidney ports 56 a and 56 b, and isnot-relatively rotatably fitted on motor shaft 127 inserted in shafthole 127 a (in a spline-engaging manner). Pistons 123 are reciprocallyslidably fitted in the respective cylinder holes of cylinder block 120,and project at heads thereof outward from cylinder block 120 so as toabut against a fixed swash plate M1 a.

As shown in FIG. 17, motor shaft 127, rotatably fitted at a right endportion thereof in shaft hole 127 a of center section 101, is journalledthrough a bearing 128 by the partition wall between the hydrauliccircuit chamber and the transmission gear chamber, and extended at aleft end portion thereof into the transmission gear chamber so as to beprovided thereon with a gear 127 b and a brake disc 140.

Referring to FIGS. 17 and 18, rear motor kidney port 56 a is connectedto right pump kidney port 57 a through horizontal fluid passage hole(passage) 21, as mentioned above. Referring to FIGS. 18 and 24( b), thepart of passage 22 bored in center section 101 comprises fluid passageholes 22 c and 22 d, and the part of passage 22 bored in charge pumpcasing 102 is a fluid passage hole 22 b. Fluid passage hole 22 d isfore-and-aft horizontally extended in a front portion of center section101, and connected at an upper portion thereof to front motor kidneyport 56 b. Vertical fluid passage hole 22 c is extended from fluidpassage hole 22 d, and opened downward at the bottom surface of centersection 101 just in front of fluid passage hole 27 c, so as to bedirectly coaxially to vertical fluid passage hole 22 b bored in chargepump casing 102.

Referring to FIG. 18, center section 101 is bored in a rear portionthereof with a vertical fluid passage hole serving as passage 34, andprovided therein with upper and lower charge check valves 35 interposedbetween fluid passage hole 34 and respective upper and lower parallelfluid passage holes 21 and 27 d. Each of charge check valves 35 allowsonly flow from fluid from fluid passage hole (passage) 34 tocorresponding fluid passage hole (passage) 21 or 27 d (i.e., preventsbackflow to fluid passage hole 34). Fluid passage hole 34 is openeddownward at the bottom surface of center section 101, and connected anupwardly opened fluid passage hole 99 c of passage 99 bored in chargepump casing 102.

Referring to FIG. 18, charge pump casing 102 is fastened to centersection through bolts 150. Referring to FIGS. 20, 24(a) and 24(b),charge pump casing 102 is provided at a bottom portion with a downwardlyopened vertical pin hole, which coaxially coincides with an upwardlyopened vertical pin hole bored in a bottom portion of rear transaxlehousing 1H. A lock pin 152 is fitted in the coinciding pin holes ofcharge pump casing 102 and rear transaxle housing 1H, so as to engagecharge pump casing 102 to rear transaxle 1H at a determined position.

Referring to FIG. 18, as mentioned above, upwardly opened vertical fluidpassage hole 22 b and 27 b are bored in charge pump casing 102 so as tobe coaxially connected to respective vertical fluid passage holes 22 cand 27 c bored in center section 101. Referring to FIGS. 18, 19, 20 and24(a), front and rear laterally horizontal joint plugs 22 a and 27 a arescrewed into charge pump casing 102 so as to be connected to respectivefluid passage holes 22 b and 27 b. Right end portions of joint plugs 22a and 27 a project rightwardly outward from the right side surface ofcharge pump casing 102, and from the right side surface of reartransaxle housing 1H, so as to be provided with respective rightwardlyoutward opened ports 1 a and 1 b. In this way, passage 22 betweenhydraulic pump P (pump kidney port 57 b) and port 1 a in rear transaxlehousing 1H is constituted by the series of fluid passage holes 22 d, 22c, 22 b and joint plug 22 a, while passage 27 between hydraulic motor M1(motor kidney port 56 b) and port 1 b in rear transaxle housing 1H isconstituted by the series of fluid passage holes 27 e, 27 d, 27, 27 band joint plug 27 a. Incidentally, front joint plug 22 a with port 1 ais higher than rear joint plug 27 a with port 1 b. In this regard,vertical fluid passage hole 27 b is bored deeper than vertical fluidpassage hole 22 b.

Referring to FIG. 24( a), charge pump casing 102 is bored with avertical circular cylindrical trochoid gear chamber 137 which is openedupward to face the bottom surface of center section 101. Referring toFIGS. 21 and 24( a), a circular (in plan view) shaft hole 137 a, intowhich the lower portion of input shaft 17 is rotatably inserted, isextended downward from a bottom center portion of trochoid gear chamber137. Charge pump casing 102 is bored from the bottom surface of trochoidgear chamber 137 with a vertical suction port 58 a on the left side ofshaft hole 137 a, and with a vertical delivery port 58 b on the rightside of shaft hole 137 a. Referring to FIG. 21, a trochoid gearconsisting of an inner gear 135 and an outer gear 136 is disposed ingear chamber 137. Inner gear 135 is fixed on input shaft 17 inserted inshaft hole 137 a, so as to be rotatable integrally with input shaft 17.

Referring to FIGS. 23 and 24( a), a fore-and-aft horizontal fluidpassage hole serving as suction passage 31 is bored in charge pumpcasing 102, connected at a rear end thereof to suction port 58 a, andforwardly outward opened at a recess 32 d formed on the front sidesurface of charge pump casing 102. Horizontal fluid filter 32 is fittedat a rear end thereof into recess 32 d so as to be fluidly connected tosuction passage hole 31.

Referring to FIGS. 21 and 24( a), a lateral horizontal fluid passagehole 98 b serving as a part of passage 98 is bored in charge pump casing102, connected at a left end thereof to delivery port 58 b, andconnected at a right end thereof to a lateral horizontal joint plug 98 ascrewed into charge pump casing 102. A right end portion of joint plug98 a projects rightwardly outward from the right side surface of chargepump casing 102, and from the right side surface of rear transaxlehousing 1H, so as to be provided with rightwardly outward opened port75. In this way, passage 98 interposed between the delivery port ofcharge pump 33 and port 75 is constituted by fluid passage hole 98 b andjoint plug 98 a.

Referring to FIGS. 24( a) and 24(b), a downwardly opened groove ofcharge pump casing 101 and an upwardly opened groove of charge pump 102along a right side edge of trochoid gear chamber 137 coincide with eachother so as to form a substantially fore-and-aft fluid passage hole 99c. Referring to FIGS. 22 and 24( a), a lateral horizontal fluid passagehole 99 b is bored in charge pump casing 102 leftwardly upward fromfluid passage hole 98 b, connected at a left end portion thereof to anintermediate portion of fluid passage hole 99 c, and connected at aright end portion thereof to a joint plug 99 a screwed into charge pumpcasing 102. A right end portion of joint plug 99 a projects rightwardlyoutward from the right side surface of charge pump casing 102, and fromthe right side surface of rear transaxle housing 1H, so as to beprovided with rightwardly outward opened port 76.

Referring to FIGS. 18 and 24( b), the bottom opening of vertical fluidpassage hole 34 is connected to a rear end portion of fluid passage hole99 c. As mentioned above, in center section 101, fluid passage hole 34is connected to fluid passage holes 21 and 27 d through respectivecharge check valves 35. In this way, joint plug 99 a and fluid passageholes 99 b and 99 c constitute passage 99 interposed between port 76 andeither lower pressurized passage 21 or 27 connected to the suction sideof hydraulic pump P through corresponding charge check valve 35.

Referring to FIGS. 18 and 24( a), check valve 39 is disposed at a frontend portion of fluid passage hole 99 c. A fluid passage hole 50 a isextended from an intermediate portion of fluid passage hole 99 c torelief valve 50. Referring to FIGS. 22 and 24( a), a fluid passage hole36 b from a relief valve 36 is connected to a bottom portion of fluidpassage hole 99 c joining fluid passage hole 99 b. Check valve 39,relief valve 50 and relief valve 36 will be detailed later.

The above arrangement of rear transaxle 1 shown in FIGS. 16 to 24 isassociated with the arrangement of vehicle 100 shown in FIG. 3 or 9, sothat ports 1 a, 1 b, 75 and 76 are provided on the respective rightouter ends of joint plugs 22 a, 27 a, 98 a and 99 a projectingrightwardly outward from charge pump casing 102 through the right sidewall of rear transaxle housing 1H. Therefore, pipes 23, 26, 81 and 82can be compactly collected to be connected to respective ports 1 a, 1 b,75 and 76. Alternatively, for the arrangement of vehicle 100 shown inFIG. 5, rear transaxle 1 may be disposed so that ports 1 a, 1 b, 75 and76 are provided on the respective left outer ends of joint plugs 22 a,27 a, 98 a and 99 a projecting leftwardly outward from charge pumpcasing 102 through the left side wall of rear transaxle housing 1H.

As shown in FIG. 16, front axle-driving hydraulic fluid port 1 a isdisposed higher than rear axle-driving hydraulic fluid port 1 b, andfront auxiliary (power steering) device driving hydraulic fluid port 75is disposed lower than rear auxiliary (power steering) device drivinghydraulic fluid port 76. Due to the height difference, ports 1 a, 1 b,75 and 76 are disposed compactly in the fore-and-aft direction, andpipes 23, 27, 81 and 82 connected these ports can be smoothly extendedforwardly upward without stressing bend, thereby being further compactlycollected.

A mechanism for controlling the tilt angle and direction of movableswash plate Pa of hydraulic pump P will be described. Referring to FIG.21, a horizontal control shaft 113 rotatably penetrates a right sidewall of rear transaxle housing 1H. A control arm 114 is fixed on aninner end of control shaft 113 inside housing 1H and engages at a topportion thereof with swash plate Pa. Speed control lever 14 operativelyconnected to speed control pedal 13 is fixed on control arm 114 outsidehousing 1H.

Referring to FIGS. 21 and 23, a torque spring 115 is wound aroundcontrol shaft 113 inside housing 1H and includes twisted and extendedopposite end portions, so as to pinch a pin (not shown) fixed on controlarm 114 and a retaining pin 117 planted into the right side wall ofhousing 1H. Referring to FIGS. 16 and 21, retaining pin 117 projectsoutward from housing 1H so as to be provided thereon with a nut 116 forfastening retaining pin 117 to housing 1H. Unless speed control pedal 13is depressed, the force of spring 115 pinching both retaining pin 117and the pin fixed on arm 114 keeps swash plate Ma at the neutralposition. When speed control pedal 13 is depressed on either front orrear side thereof, swash plate Pa is tilted integrally with the rotationof lever 14, shaft 113 and arm 114 so that spring 115 pushes the pinfixed on arm 114 at one end thereof away from retaining pin 117retaining the other end thereof, so as to generate the neutral-returningbiasing force. Due to the neutral-returning biasing force of spring 115,swash plate Pa is kept at the tilt position corresponding to thedepression angle and direction of speed control pedal 13, and, if speedcontrol pedal 13 is released from depression force, swash plate Pa andspeed control pedal 13 return to the respective neutral positions.

The flow of fluid in HST circuit HC1, especially in rear transaxle 1,during forward traveling will be described. By depressing speed controlpedal 13 in the direction for forward traveling, swash plate Pa ofhydraulic pump P is tilted from the neutral position (where swash platePa is disposed perpendicular to input shaft 17, as shown in FIG. 23) toa position corresponding to the depression degree and direction of speedcontrol pedal 13. In this state, cylinder block 104 is rotatedintegrally with input shaft 17 so as to reciprocate pitons 109 at astroke corresponding to the tilt angle of movable swash plate Pa,whereby hydraulic pump P sucks fluid from right pump kidney port 57 ainto the cylinder holes of cylinder block 104, and delivers fluid fromthe cylinder holes to left pump kidney port 57 b.

Referring to FIGS. 2, 3, 18 and 20, fluid in pump kidney port 57 b fromhydraulic pump P is led to port 1 b through passage 27 consisting offluid passage holes 27 e, 27 d, 27 c and 27 b and joint plug 27 a. Inthis state, corresponding charge check valve 35 preventshigh-pressurized fluid in passage 27 from entering charge fluid passage34. Fluid flows from port 1 b of rear transaxle 1 to hydraulic motors M2and M3 in front transaxle 2 through pipe 26, and returns to port 1 a ofrear transaxle 1 through pipe 23. Referring to FIGS. 18 and 19, in reartransaxle 1, fluid is introduced into front motor kidney port 56 bthrough passage 22 consisting of joint plug 22 a and fluid passage holes22 b, 22 c and 22 d. Referring to FIG. 17, fluid is introduced fromfront motor kidney port 56 b into the cylinder holes of cylinder block120 of hydraulic motor M1 so as to reciprocate pitons 123 at a strokecorresponding to the tilt angle of fixed swash plate Ma, therebyrotating cylinder block 120 with motor shaft 127 for forward travelingrotation. Referring to FIGS. 17, 18 and 20, the fluid in the cylinderholes of cylinder block 120 is delivered into rear motor kidney port 56a, and returns through passage 21 to right pump kidney port 57 a servingas the suction port of hydraulic pump P. In this state, correspondingcharge check valve 35 prevents high-pressurized fluid in passage 21 fromentering charge fluid passage 34.

When speed control pedal 13 is depressed in the direction for backwardtraveling, the above fluid flow route is reversed. That is, left pumpkidney port 57 b serves as the suction port of hydraulic pump P, andright pump kidney port 57 a serves as the delivery port of hydraulicpump P, so as to rotate motor shaft 127 for backward traveling rotation.

The fluid flow concerned to charge pump 33 will be described withreference to FIGS. 2, 21 and 23. The trochoid gear consisting of innerand outer gears 135 and 136, serving as charge pump 33, is driven byinput shaft 17 so as to suck fluid from the fluid sump in rear transaxlehousing 1H into trochoid gear chamber 137 through fluid filter 32,suction passage hole 31 and suction port 58 a. Charge pump 33pressurizes fluid in trochoid gear chamber 137 and delivers it todeliver port 58 b. Relief valve 50 regulates the pressure of deliveryfluid from deliver port 58 b so as to correspond to the power steeringdevice. The pressure-regulated fluid from relief valve 50 is led intoport 75 through passage 98 consisting of fluid passage hole 98 b andjoint plug 98 a, and supplied from port 75 to power steering hydraulicvalve 80 through pipe 81. Fluid drained from valve 80 returns to port 76of rear transaxle 1 through pipe 82. Fluid is supplied from valve 80 toone chamber of power steering cylinder 79 through either pipe 83 or 84,and simultaneously drained to the other chamber of power steeringcylinder 79 through the other pipe 84 or 83, thereby telescoping pistonrod 90 of cylinder 79.

Referring to FIGS. 18, 20 and 24(b), fluid returned from valve 80 toport 76 is introduced to charge fluid passage 34 through passage 99consisting of joint plug 99 a and fluid passage holes 99 b and 99 c, andsupplied to either lower-pressurized passage 21 and pump kidney port 57a, during forward traveling, or lower-pressurized passage 27 and pumpkidney port 57 b, during backward traveling, through correspondingcharge check valve 35.

The power transmission mechanism in rear transaxle 1 between motor shaft127 and axles 6 will be detailed with reference to FIG. 17. Decelerationgear train 37 comprises a diametrically large gear 37 a, a diametricallysmall gear 37 b, a counter shaft 37 c and a sleeve 37 d. In thetransmission gear chamber of rear transaxle housing 1H, laterallyhorizontal counter shaft 37 c is fixedly spanned between the left sidewall of housing 1H and the partition wall in housing 1H behind motorshaft 127 and in front of axles 6. Sleeve 37 d is relatively rotatablyprovided on counter shaft 37 c, and diametrically large and small gears37 a and 37 b are fixed on sleeve 37 d. Large gear 37 a meshes with gear127 b fixed on motor shaft 127, and small gear 37 b meshes with a bullgear 38 a of differential gear unit 38.

Differential gear unit 38 comprises bull gear 38 a, a pair of left andright differential side gears 38 b, and pinions 38 c. Differential sidegears 38 b are not-relatively rotatably (spline-fittingly) provided onrespective proximal end portions of left and right axles 6. Pinions 38 care relatively rotatably supported in bull gear 37 a, so as to havepivots disposed in the radial direction of bull gear 37 a. Each pinion38 c meshes with both differential side gears 38 b, so as todifferentially distribute the rotary force of bull gear 37 a betweenleft and right axles 6.

Referring to FIG. 19, a vertical brake camshaft 143 is rotatablysupported in rear transaxle housing 1H. A brake arm 142 is fixed on atop portion of brake camshaft 143 projecting upward from rear transaxlehousing 1H, and operatively connected to brake pedal 41 through alinkage. In rear transaxle housing 1H, brake camshaft 142 is formed at avertically intermediate portion thereof with a sectionallysemicircularly shaped cam 144 facing brake disc 140 on motor shaft 127through a brake shoe 141. When brake pedal 41 is depressed, brake arm142 and brake camshaft 143 are integrally rotated, so as to slant cam144 when viewed in plan, and press brake shoe 141 against brake disc140, thereby braking motor shaft 127.

A safety valve device for the hydraulic circuit system will be describedwith reference to FIGS. 18, 20 and 24(a). As mentioned above, checkvalve 39 is disposed at the front end of fluid passage hole 99 c incharge pump casing 102. In charge pump casing 102, a vertical fluidpassage hole 39 a is extended downward from check valve 39, and aleftwardly horizontal fluid passage hole 39 b is extended leftward froma bottom portion of vertical fluid passage hole 39 a, so as to beconnected to suction passage hole 31.

When vehicle 100 is parked on a slope, hydraulic motor M1 receivesbackflow driving force from wheels 7 and acts as a pump so as toexcessively pressurize HST circuit HC1. Hydraulic pump P and charge pump33 are not driven, and movable swash plate Pa of pump P is disposed atthe neutral position. However, due to the excessive pressurization byhydraulic motor M1, fluid leaks from the gap between hydraulic pump Pand pump contact surface 103 or the gap between hydraulic motor M1 andmotor contact surface 129. Consequently, HST circuit HC1 becomes shortof fluid so as to cause unexpected free rotation of hydraulic motor M1,i.e., cause the free wheel phenomenon that vehicle 100 unexpectedlydescends the slope. Therefore, when HST circuit HC1 is hydraulicallydepressed by the fluid leak, check valve 39 is automatically opened topass fluid from the fluid sump in rear transaxle housing 1H to either orboth of passage 21 and 27 through check valve or valves 35. In this way,even while charge pump 33 is inactivated, check valve 39 supplies HSTcircuit HC1 with fluid so as to prevent the free wheel phenomenon.

Referring to FIGS. 22 and 23, charge pump casing 102 is bored in a leftrear portion thereof with a lateral horizontal circular hole, into whichpressure-regulating relief valve 36 is fitted. A horizontal fluidpassage hole 36 a is extended rightward from the upstream side of reliefvalve 36, and a vertical fluid passage hole 36 b is extended upward fromfluid passage hole 36 a to fluid passage hole 99 c, so as to connect theupstream side of relief valve 36 to lower-pressurized passage 99 (fluidpassage hole 99 c). A vertical fluid passage hole 36 c is extendeddownward from the downstream side of charge pump 36 and downwardlyoutwardly opened at the bottom surface of charge pump casing 102 to thefluid sump in rear transaxle housing 1H. When the charge fluid circuitis excessively supplied with fluid and the pressure in passage 99excesses a predetermined level, relief valve 36 is opened to drain fluidfrom passage 99 to the fluid sump outside of charge pump casing 102through fluid passage holes 36 b, 36 a and 36 c, thereby keeping theproper pressure level of fluid charged to the axle-driving hydraulicfluid circuit in HST circuit HC1.

Referring to FIGS. 18 and 20, charge pump casing 102 is bored in a rearbottom portion thereof with a fore-and-aft horizontal circular hole,into which pressure-regulating relief valve 50 for regulating pressurein the auxiliary (e.g., power steering) device driving fluid circuit isfitted. The upstream side of relief valve 50 is connected tohigher-pressurized fluid passage hole 98 b, and the downstream side ofrelief valve 50 is connected to lower-pressurized fluid passage hole 99c through a vertical fluid passage hole 50 a. In the auxiliary devicedriving fluid circuit, if higher-pressurized passage 98 is excessivelypressurized, relief valve 50 is opened to bypass fluid fromhigher-pressurized passage 98 to lower-pressurized passage 99.

Referring to FIG. 19, rear transaxle 1 is provided with a forciblerelief valve 160 comprising a lever 161, a camshaft 162, and a pushpin163. Vertical camshaft 163 is rotatably fitted at a cam-shaped bottomportion into center section 101. Horizontal pushpin 163 is axiallyslidably disposed in center section 101 between motor contact surface129 and the cam portion of camshaft 163. Horizontal lever 161 is fixedon a top portion of camshaft 162 projecting upward from rear transaxlehousing 1H. When vehicle 100 is towed, wheels 7 and 9 are requested torotate freely from the hydraulic pressure in HST circuit HC1. Therefore,lever 161 is manually rotated together with camshaft 162 so that the camportion of camshaft 162 thrusts pushpin 163 outward from motor contactsurface 129, thereby pushing and separating cylinder block 120 frommotor contact surface 129, and draining fluid from motor kidney ports 56a and 56 b to the fluid sump in rear transaxle housing 1H. In this way,fluid in HST circuit HC1 is reduced so as to allow the free rotation ofwheels 7 and 9.

Rear transaxle 1 is provided with a mechanism for expanding the neutraldead zone of hydraulic pump P relative to the tilt of movable swashplate Pa. Referring to FIG. 21, in center section 101, upper and lowerhorizontal fluid passage holes 171 and 172 are extended rightward fromrespective upper and lower fluid passage holes 21 and 27 d, and openedrightwardly outward at the right side surface of center section 101. Apair of upper and lower plugs provided at right end portions withrespective rightwardly outward opened orifices 171 a and 172 a arefitted leftward into upper and lower fluid passage holes 171 and 172,and project at the right end portions thereof from the right openings offluid passage holes 171 and 172 on the right side surface of centersection 101. A portion of control arm 114 opposite to the end engaged toswash plate Pa with respect to control shaft 113 is extended so as toabut against the right end of the plugs. A groove 114 a constantlyopened to the fluid sump in rear transaxle housing 1H is formed on thesurface of the extended portion of control arm 114 facing the plugs soas to correspond to a tilt range of swash plate Pa for making theexpanded neutral dead zone of hydraulic pump P.

While swash plate Pa is disposed within the tilt range including theneutral position so that either or both of orifices 171 a and 172 a areopened to groove 114 a (in FIG. 21, both orifices 171 a and 172 a areopened to groove 114 a), a certain amount of fluid is drained fromhigher-pressurized passage 21 or 27 to the fluid sump through orifice171 a or 172 a and groove 114 a, so as to prevent hydraulic pump P fromsupplying fluid to hydraulic motors M1, M2 and M3, thereby ensuring theextended neutral dead zone of hydraulic pump P for preventing vehicle100 from moving. The tilt angle of movable swash plate Pa with controlarm 114 from the neutral position is increased so as to take groove 114a apart from both orifices 171 a and 172 a, both the right end openingsof orifices 171 a and 172 a are closed by the surface of the extendedportion of control arm 114 so as to prevent fluid from being drainedfrom higher-pressurized passage 21 or 27, thereby ensuring the propervolumetric efficiency between hydraulic pump P and hydraulic motors M1,M2 and M3.

Alternatively, to expand the tilt range for the neutral dead zone ofhydraulic pump P, a check and neutral valve may be interposed betweenpassages 21 and 27.

Alternatively, referring to FIG. 25, a pump housing PH incorporatinghydraulic pump P and charge pump 33 is disposed outside of reartransaxle housing 1H which incorporates hydraulic motor M1, decelerationgear train 37, differential gear unit 38 and axles 6.

Referring to FIG. 25, port 1 a connected to external pipe 23 is disposedon rear transaxle housing 1H, and hydraulic motor M1 is connected toport 1 a through passage 22 in rear transaxle housing 1H. Port 1 bconnected to external pipe 26 is disposed on an outer surface of pumphousing PH, and hydraulic pump P is connected to port 1 b throughpassage 27 in pump housing PH. An outward opened port 77 a is disposedon an outer surface of pump housing PH, and a port 77 c is disposed onan outer surface of rear transaxle housing 1H. Passage 21 is disposed inpump housing PH, and interposed between hydraulic pump P and port 77 a.A passage 77 d is disposed in rear transaxle housing 1H, and interposedbetween hydraulic motor M1 and port 77 c. An external pipe 77 b isdisposed outside of pump housing PH and rear transaxle housing 1H, andinterposed between ports 77 a and 77 c. Ports 75 and 76 connected torespective external pipes 81 and 82 are disposed on the same outer sidesurface of pump housing PH with port 1 a. In pump housing PH aredisposed the charge fluid circuit portion between fluid filter 32 andport 75 through charge pump 33 and passage 98, the charge fluid circuitportion between port 76 and passages 21 and 27 through passage 99 andcharge check valves 35, and associate valves and equipments, which aredisposed in rear transaxle housing 1H in the embodiment of FIG. 2.

Pump housing PH is disposed adjacent to rear transaxle housing 1H (e.g.,just in front of housing 1H or just above housing 1H). Preferably, ports1 b, 75 and 76 are disposed on a right side surface of pump housing PHwhile port 1 a is disposed on the right side surface of rear transaxlehousing 1H, thereby collecting ports 1 a, 1 b, 75 and 76 at the rightside of vehicle 100 so as to compactly collect pipes 23, 26, 81 and 82.Alternatively, if port 1 a is disposed on the left side surface of reartransaxle housing 1H, ports 1 b, 75 and 76 are disposed on the left sidesurface of pump housing PH.

Alternative arrangements of joint plugs 22 a and 27 a having respectiveports 1 a and 1 b fitted into rear transaxle housing 1H will bedescribed with reference to FIGS. 33( a) and 33(b) (each of FIGS. 33( a)and 33(b) illustrates only representative joint plug 22 a). Joint plugs22 a and 27 a are provided thereon with respective O-rings 175 inrespective plug holes through the wall of rear transaxle housing 1H.Further, referring to FIG. 33( a), each of the plug holes within thewall of rear transaxle housing 1H is tapped, and each of joint plugs 22a and 27 a has an intermediate threaded portion corresponding to thetapped plug hole, so as to be immovably fastened to rear axle housing1H, while each of joint plugs 22 a and 27 a are slidably fitted intocharge pump casing 102. Due to the screw-engagement of joint plugs 22 aand 27 a to rear transaxle housing 1H, joint plugs 22 a and 27 a areprevented from being axially deviated by movement of pipes 23 and 26according to the swing of front transaxle 2 around center pivot 5,thereby preventing fluid leak from the gap between O-ring 175 and theperipheral wall surface of the shaft hole in rear transaxle housing 1H.Referring to FIG. 33( b), for the same purpose of the arrangement ofFIG. 33( a), a flange 176 is fixed on the outer peripheral portion ofeach of joint plugs 22 a and 27 a projecting outward from rear axlehousing 1H, and flange 176 is fastened onto the outer side surface ofrear transaxle housing 1H through bolts or screws. In this way, thearrangements shown in FIGS. 33( a) and 33(b) improve the fluid tightnessof joint plugs 22 a and 27 a against rear transaxle housing 1H.

Alternatively, vehicle 100 may be provided at a front portion thereofwith transaxle 1 incorporating hydraulic motor M1, deceleration geartrain 37 and differential gear unit 38, and provided at a rear portionthereof with transaxle 2 incorporating hydraulic motors M2 and M3. Inthis regard, front wheels may be unsteerable, and rear wheel may besteerable.

Second Embodiment

Each of hereinafter described vehicles 200 and 300 is provided withfront transaxle 2 in which positions or directions of ports 2 a and 2 bare different from those of front transaxle 2 of vehicle 100. Referringto FIG. 10, vehicle 200 according to a second embodiment is providedwith front transaxle 2 serving as laterally reversed front transaxle 2of vehicle 100. Namely, in front transaxle 2 of this embodiment, rightfixed displacement hydraulic motor M2 and left variable displacementhydraulic motor M3 are disposed in front transaxle housing 2H. In thisregard, cam mechanism CM for controlling the tilt of swash plate M3 a ofhydraulic motor M3 is disposed leftward in front transaxle 2. Ports 2 aand 2 b are disposed on a laterally intermediate rear portion of reartransaxle housing 2H so as to be rightwardly outward opened. Further,referring to FIG. 10, ports 1 a and 1 b are disposed on the right sidesurface of rear transaxle housing 1H. Vehicle 200 employs HST circuitHC1 similar to that of FIG. 2.

To corresponding to rightward ports 2 a and 2 b on front transaxle 2,pipes 23 and 26 interposed between respective rear ports 1 a and 1 b andrespective front ports 2 a and 2 b include fore-and-aft main portionsextended along right side plate 3R of frame 3 (along the bottom edge ofright side plate 3R when viewed in side, and along the inside surface ofright side plate 3R when viewed in plan). Pipe 23 includes rear rigidpipe 23 b connected to port 1 a, front rigid pipe 23 c connected to port2 a, and flexible hose 23 a interposed between rear and front rigidpipes 23 b and 23 c. Pipe 26 includes rear rigid pipe 26 b connected toport 1 b, front rigid pipe 26 c connected to port 2 b, and flexible hose26 a interposed between rear and front rigid pipes 26 b and 26 c. Rearrigid pipes 23 b and 26 b are extended rightward from respective ports 1a and 1 b, bent and extended forwardly upward, and bent against andextended horizontally forward, so as to be clamped by clamping stay 62fixed on the inside surface of right side plate 3R. Front rigid pipes 23c and 26 c are extended in the fore-and-aft direction along right sideplate 3R of frame 3 (along the bottom edge of right side plate 3R whenviewed in side, and along the inside surface of right side plate 3R whenviewed in plan), and connected to respective rear rigid pipes 23 b and26 b through respective swivel joints 54, and to respective front rigidpipes 23 c and 26 c through respective swivel joints 55. Thisarrangement of pipes 23 and 26 serves as the laterally reversedarrangement of pipes 23 and 26 shown in FIG. 5 where ports 1 a and 1 bare disposed on the left side surface of rear transaxle housing 1H andports 2 a and 2 b are disposed on the left side surface of fronttransaxle housing 2H. Further, tension pulley 52 with spring 53 alsoserves as the laterally reversed tension pulley 52 shown in FIG. 3 so asto be prevented from interfering with pipes 23 and 26 along right sideplate 3R.

This arrangement of pipes 23 and 26 between rear and front transaxles 1and 2 has the same advantages as the arrangement of pipes 23 and 26shown in the embodiment of FIG. 3 combined with the embodiment of FIG.5. That is, pipes 23 and 26 can be compactly disposed at the safe spaceinside frame 3 while they are prevented from interfering with thetraveling power transmission system, the mower-driving powertransmission system and mower unit 20, from having fluid leak and beingdamaged at ends thereof connected to ports 1 a, 1 b, 2 a and 2 b, andfrom being subjected to twisting stress caused by the swing of fronttransaxle 2 around center pivot 5. Further, since all rear ports 1 a and1 b and front ports 2 a and 2 b are disposed rightward, rear rigid pipes23 b and 26 b have no laterally extended portions disposed just in frontof rear transaxle housing 1H, i.e., have bent portions reduced.

Referring to FIG. 10, power steering valve 80 (not shown) is disposed onframe 3 between rear and front transaxles 1 and 2, power steeringcylinder 79 is attached onto the outside surface of right side plate 3R,and ports 75 and 76 are disposed on the right side surface of reartransaxle housing 1H. Therefore, pipes 81 and 82 are disposed alongpipes 23 and 26 along right side plate 3R. The arrangement of pipes 81,82, 83 and 84 for power steering serves as the laterally reversedarrangement of those shown in FIG. 5. Further, in association with theposition of power steering cylinder 79 rightward of frame 3, bracket 48a pivotally connected to piston rod 90 of cylinder 79 is provided onright front wheel support unit 48R in association with cam mechanism CMdisposed leftward on front transaxle 2. Other structure and parts invehicle 200 are similar to vehicle 100 whose rear portion is configuredas shown in FIG. 5.

Referring to FIG. 11, in vehicle, pipes 23 and 26 interposed betweenrightward opened ports 1 a and 1 b of rear transaxle 1 and rightwardopened ports 2 a and 2 b of front transaxle 2 comprise flexible pipes 23d and 26 d connected to ports 2 a and 2 b and rigid pipes 23 e and 26 econnected to ports 1 a and 1 b. Rigid pipes 23 e and 26 e are extendedalong right side plate 3R, clamped by clamping stays 62 and 63 fixed toright side plate 3R, and connected at front ends thereof to respectiverigid pipes 23 d and 26 d through respective swivel joints 55. Thisarrangement of pipes 23 and 26 serves as the laterally reversedarrangement of pipes 23 and 26 shown in FIG. 9, excluding that flexiblehoses 23 e and 26 e do not have laterally extended portions disposedjust in front of rear transaxle housing 1H because ports 1 a and 1 b aredisposed on the right side surface of rear transaxle housing 1H. Theincrease of rigid pipe portions in pipes 23 and 26 advantageouslyreduces internal pressure resistance in pipes 23 and 26.

Third Embodiment

Referring to FIGS. 12 and 13, each of vehicles 300 according to a thirdembodiment is provided with front transaxle 2 substantially similar tofront transaxle 2 of vehicle 100 shown in FIG. 3. That is, fronttransaxle housing 2H incorporates left fixed displacement hydraulicmotor M2 and right variable displacement hydraulic motor M3, cammechanism CM is disposed in the rightward portion of front transaxle 2,and port 2 a connected to pipe 23 is rightwardly outward opened. Thedifferent point of rear transaxle 2 of vehicle 300 from that of vehicle100 is that port 2 b connected to pipe 26 is rightwardly outward openedopposite to port 2 a. Further, referring to FIGS. 12 and 13, ports 1 aand 1 b are disposed on the right side surface of rear transaxle housing1H.

Referring to FIGS. 12 and 13, to correspond to this arrangement of ports1 a, 1 b, 2 a and 2 b, arrangement of pipe 23 interposed between ports 1a and 2 a is similar to that of vehicle 100 shown in FIG. 3, andarrangement of pipe 26 interposed between ports 1 b and 2 b is similarto that of vehicle 200 shown in FIG. 10. That is, pipe 23 includes thefore-and-aft main portion extended along left side plate 3L (along thebottom edge of left side plate 3L when viewed in side and along theinside surface of left side plate 3L when viewed in plan), and pipe 26includes the fore-and-aft main portion extended along right side plate3R (along the bottom edge of right side plate 3R when viewed in side andalong the inside surface of right side plate 3R when viewed in plan). Inassociation with the laterally opposite arrangement of ports 1 a and 2a, pipe 23 includes the lateral extended portion disposed just in frontof rear transaxle housing 1H (and clamped by clamping stay 60 fixed onrear transaxle housing 1H) so as to be extended at the fore-and-aft mainportion thereof along left side plate 3L. On the other hand, since bothports 1 b and 2 b are opened rightward, pipe 26 is extended from port 1b to the fore-and-aft main portion thereof without bending to have alateral extended portion just in front of rear transaxle housing 1H.

More specifically, referring to FIG. 12, pipe 23 comprises rear andfront rigid pipes 23 b and 23 c and flexible hose 23 a interposedbetween rigid pipes 23 b and 23 c, and pipe 26 comprises rear and frontrigid pipes 26 b and 26 c and flexible hose 26 a interposed betweenrigid pipes 26 b and 26 c. Flexible hose 23 a is extended in thefore-and-aft direction along left side plate 3L, connected at the rearend thereof through swivel joint 54 to rear rigid pipe 23 b connected toport 1 a, and connected at the front end thereof through swivel joint 55to front rigid pipe 23 c connected to port 2 a. Flexible hose 26 a isextended in the fore-and-aft direction along right side plate 3R,connected at the rear end thereof through swivel joint 54 to rear rigidpipe 26 b connected to port 1 b, and connected at the front end thereofthrough swivel joint 55 to front rigid pipe 26 c connected to port 2 b.Rear rigid pipe 23 b includes the lateral extended portion which isdisposed just in front of rear transaxle housing 1H and clamped byclamping stay 60 fixed on rear transaxle housing 1H. The forwardlyextended front portion of rear rigid pipe 23 b is clamped by clampingstay 61 fixed to left side plate 3L so as to be connected to flexiblehole 23 a through swivel joint 54. Rear rigid pipe 26 b includes nolateral extended portion disposed just in front of rear transaxlehousing 1H, but is extended substantially forward when viewed in plan soas to be connected to flexible hose 26R through swivel joint 54.

Referring to FIG. 13, pipe 23 comprises flexible hose 23 d connected toport 2 a, and rigid pipe 23 e connected to port 1 a. Pipe 26 comprisesflexible hose 26 d connected to port 2 b, and rigid pipe 26 e connectedto port 1 b. Rigid pipe 23 e includes the fore-and-aft extended portionalong left side plate 3L, and is connected at the rear end thereof toport 1 a, and at the front end thereof to flexible hose 23 d throughswivel joint 55. Further, rigid pipe 23 e includes the lateral extendedportion which is disposed just in front of rear transaxle housing 1H andclamped by clamping stay 60 fixed on rear transaxle housing 1H. Thefront portion of rigid pipe 23 e is clamped by clamping stay 61 fixed toleft side plate 3L so as to be connected to flexible hose 23 d throughswivel joint 55. Rigid pipe 26 e includes the fore-and-aft extendedportion along right side plate 3R, and is connected at the rear endthereof to port 1 b, and at the front end thereof to flexible hose 26 dthrough swivel joint 55. Rigid pipe 26 e includes no lateral extendedportion disposed just in front of rear transaxle housing 1H, but isextended substantially forward when viewed in plan so as to be disposedalong right side plate 3R, and connected at the front end thereof toflexible hose 26 d through swivel joint 55.

Other features and advantages in these arrangements of pipes 23 and 26in FIGS. 12 and 13 are the same as those in the above descriptions aboutthe embodiments of FIGS. 3, 9, 10 and 11.

Further, referring to FIGS. 12 and 13, power steering device 80 isdisposed between rear and front transaxles 1 and 2, and power steeringcylinder 79 is disposed along left side plate 3L and includes piston rod90 connected to bracket 48 a mounted on left front wheel support unit48L. Ports 76 and 78 are disposed on the same right side surface of reartransaxle housing 1H with ports 1 a and 1 b. In this condition, pipes 81and 82 interposed between valve 80 and respective ports 75 and 76, andpipes 83 and 84 interposed between valve 80 and cylinder 79 are disposedsimilar to those in the arrangement of FIG. 3. In this regard, pipes 81and 82 are disposed along pipe 26 along right side plate 3R. Thefeatures and advantages of the arrangement of power steering pipes arethe same as those in the above description of FIG. 3.

Alternatively, each of vehicle 300 may be provided with any of reartransaxles 1 arranged as shown in FIGS. 5, 6 and 7. If either of reartransaxles 1 shown in FIGS. 5 and 7 is equipped on vehicle 300, sinceports 1 a and 1 b are disposed leftward of rear transaxle housing 1H,pipe 26 including the fore-and-aft main portion extended along rightside plate 3R includes the lateral extended portion disposed just infront of rear transaxle 1, and pipe 23 including the fore-and-aft mainportion extended along left side plate 3L includes no lateral extendedportion disposed just in front of rear transaxle 1. Pipes 81 and 82 aredisposed along pipe 23 along left side plate 3L.

Fourth Embodiment

Each of hereinafter described vehicles 400 and 500 is provided with areservoir tank arranged in a different manner from that of reservoirtank 28 in vehicle 100. Referring to FIG. 14, in vehicle 400 accordingto a fourth embodiment, a reservoir tank 428 is joined to a fuel tankFT. Fuel tank FT and reservoir tank 428 are disposed between reartransaxle 1 and driver's seat 16 above rear transaxle 1, i.e., belowdriver's seat 16 and above rear transaxle 1. A breather 442 of reservoirtank 428, also serving as a fluid-supply opening of reservoir tank 428,is disposed behind seat 16.

More specifically, in rear cover 15 on the rear portion of frame 3 isdisposed a tank 451 whose inner space is divided into front and rearchambers by a partition 450. The front chamber in tank 451 serves asfuel tank FT. The rear chamber serves as reservoir tank 428, which isdisposed just behind seat 16 mounted on the top of rear cover 15 in thefore-and-aft direction of vehicle 400.

The top portion of rear cover 15 is bored with a hole just behind seat16. An upright cylindrical fluid-supply portion 428 a projects upwardfrom tank 428 through the hole of rear cover 15 just behind seat 16.Breather 442 is provided on the top of fluid-supply portion 428 a.Fluid-supply portion 428 a is opened at the bottom thereof to fluid tank428 in tank 451. A fuel-supply opening is disposed on the top of fueltank FT of tank 451 under seat 16. Reservoir tank 428 is disposed sothat the fluid level in reservoir tank 428 is higher than the fluidlevels of the respective fluid sumps in rear and front transaxles 1 and2. Reservoir tank 428 is fluidly connected to the fluid sump of reartransaxle 1 through drain pipe 29, and to the fluid sump of fronttransaxle 2 through drain pipe 30, so as to absorb excessive fluid fromthe respective fluid sumps.

The integration of reservoir tank 428 with fuel tank FT is advantageousin saving the number of required parts, and facilitates assembly of thereservoir tank and the fuel tank. Due to the position of reservoir tank428 just above the rear end of frame 3, the length of drain pipe 30interposed between reservoir tank 428 and front transaxle 2 is enough toensure adequate flexibility of drain pipe 30 following the swing offront transaxle 2 around center pivot 5.

Further, referring to FIG. 14, vehicle 400 is provided with left andright mower hangers 491 whose respective pivots 92 are disposedcoaxially to axles 8 supported by rear transaxle housing 2H. Mowerhangers 491 are pivoted at top portions thereof on respective pivots 92,and extended downward. Left and right link rods 91 a are pivoted atfront ends thereof onto bottom portions of mower hangers 491, and hookedat rear ends thereof onto the front end of mower unit 20. Since pivots92 of mower hangers 491 are disposed coaxially to axles 8, the accuracyof location of mower hangers 491 is improved so as to facilitateassembly work of suspending mower unit 20.

Fifth Embodiment

Referring to FIG. 15, in vehicle 500 of a fifth embodiment, a reservoirtank 528 is disposed between rear wheels 7 and front wheels 9, and inbonnet 11 incorporating engine 10. A breather 542 of reservoir tank 528,also serving as a fluid-supply opening of reservoir tank 528, isdisposed so as to face an opening 543 provided in the dashboard at therear end of bonnet 11. Opening 543 is normally covered with a lid 543.

More specifically, in bonnet 11, reservoir tank 528 is disposed uprightjust behind engine 10 between front wheels 9 and rear wheels 7. Thebottom of reservoir tank 528 is disposed at the vertical intermediateposition of the inside of bonnet 11. A cylindrical upright fluid-supplyportion 528 a projects upward from the top of reservoir tank 528. Abreather 542, also serve as a fluid-supply opening of reservoir tank528, is disposed on the top of fluid-supply portion 528 a so as to facethe opening of the dashboard covered with lid 543. Reservoir tank 528 isfluidly connected to the fluid sump of rear transaxle 1 through drainpipe 29, and to the fluid sump of front transaxle 2 through drain pipe30, so as to absorb excessive fluid from the respective fluid sumps.

Since reservoir tank 528 is disposed between rear wheels 7 and frontwheels 9, reservoir tank 528 approaches the fore-and-aft middle portionof vehicle 500 so as to ensure good balance of vehicle 500 in thefore-and-aft direction. Due to the upright shape of reservoir tank 528,the fluid in reservoir tank 528 is prevented from being contaminatedwith air bubbles when vehicle 500 travels on a slope. Further, reservoirtank 528 disposed just behind engine 10 is easily subjected to the airfor cooling engine 10.

Further, vehicle 500 is provided with mower hangers 491 pivoted onpivots 92 disposed coaxially to axles 8, so as to suspend mower unit 20through link rods 91 a, similar to those of vehicle 400 in FIG. 14.

With respect to front transaxle 2, in each of the foregoing embodimentsof vehicles 100, 200, 300, 400 and 500, referring to FIGS. 1 to 25, thearrangement of fixed displacement hydraulic motor M2 and variabledisplacement hydraulic motor M3 for respective axles 8 may be replacedwith an arrangement of a single (variable displacement) hydraulic motorand a differential gear unit driven by the hydraulic motor. Left andright axles 8 mutually connected through the differential gear unit canbe differentially driven similar left and right axles 8 driven byrespective hydraulic motors M2 and M3. The single variable displacementhydraulic motor ensures acceleration of front wheels 9 during turning ofthe vehicle. A pair of hydraulic pressure fluid supply-and-deliveryports of the single hydraulic motor, and pipes interposed between theseports and ports 1 a and 1 b on rear transaxle 1 can be disposed on fronttransaxle housing 2H similar to any of the foregoing arrangements ofports 2 a and 2 b and pipes 23 and 26.

Sixth Embodiment

Referring to FIGS. 16 to 32, a transaxle 601 may replace rear transaxle1 in the foregoing embodiments of vehicles 100 to 500 referring to FIGS.1 to 24. Referring to FIG. 26, transaxle 601 includes housing 601H whichis provided on a right side surface thereof with ports 601 a and 601 bfor supply and delivery of hydraulic pressure fluid for driving axles,and with ports 675 and 676 for supply and delivery of hydraulic pressurefluid for driving an auxiliary (e.g., power steering) device. Ahydraulic circuit of a hydraulic four-wheel driving vehicle equippedwith transaxle 601 can be similar to the hydraulic circuit shown in FIG.2, on the assumption that a hydraulic pump P6 and a hydraulic motor M6in transaxle 601 coincide to hydraulic pump P and hydraulic motor M1 intransaxle 1, and almost other concerned parts and devices of transaxle601 coinciding to those of transaxle 1 shown in FIG. 2 are marked byrespective notations shown in FIG. 2 plus 600.

The main feature of transaxle 601 is that an adapter 693, formed thereinwith a fluid passage hole to be interposed between port 601 a and apassage in a center section 691, is detachably attached to centersection 691, as shown in FIGS. 28 and 29, and a joint plug 627 aincluding port 601 b is fitted into center section 691 to be connectedto another passage in center section 691, as shown in FIGS. 28 and 32(b).

A general structure and function of transaxle 601 will be described. Asshown in FIG. 27, the inner space of transaxle housing 601H ispartitioned by a partition wall between a hydraulic circuit chamber anda transmission gear chamber. Hydraulic pump P6 and hydraulic motor M6are disposed in the hydraulic circuit chamber, and a deceleration geartrain 637, a differential gear unit 638 and axles 6 are disposed in thetransmission gear chamber. As shown in FIGS. 26 and 29, transaxlehousing 601H is constituted by upper and lower halves joined to eachother through bolts 653.

Referring to FIG. 30, an upper portion of an input shaft 617 projectsvertically upward from transaxle housing 601H, and is fixedly providedthereon with input pulley 617 a so as to be drivingly connected toengine 10 through belt 18, and is fixedly provided thereon with coolingfan 617 b for cooling transaxle housing 601H under pulley 617 a. Intransaxle housing 601H, vertical input pulley 617 serves as the rotaryaxial shaft of hydraulic pump P6.

Variable displacement hydraulic pump P6, having input shaft 617 servingas the vertical rotary axis thereof, is vertically mounted onto a reartop surface of center section 691 at which kidney ports 657 a and 657 bare opened. As shown in FIG. 27, fixed displacement hydraulic motor M6,having a laterally (leftward) horizontal motor shaft 727 serving as therotary axis thereof, is mounted onto a front left side surface of centersection 691 at which kidney ports 656 a and 656 b are opened, so as tobe fluidly connected to hydraulic pump P6. Motor shaft 727 is drivinglyconnected to deceleration gear train 637 so as to transmit the outputforce of hydraulic motor M6 to axles 6 through deceleration gear train637 and differential gear unit 638.

As shown in FIGS. 28 and 29, vertical input shaft 617 penetrates centersection 691 and is inserted into a charge pump casing 692 attached tothe bottom surface of center section 691 so as to serve as the driveshaft of charge pump 633 in charge pump casing 692. Charge pump 633sucks fluid from the fluid sump in transaxle housing 601H so as tosupply fluid to the axle-driving hydraulic circuit, and to the auxiliarydevice (power steering) driving hydraulic circuit through ports 675 and676.

As shown in FIGS. 26 and 30, speed control lever 614 operativelyconnected to speed control pedal 13 is pivoted on transaxle housing 601Hso as to control the tilt angle and direction of a movable swash plateP6 a of hydraulic pump P6.

The structure of the hydraulic circuit system in transaxle 601 will bemore detailed. As shown in FIGS. 27 and 32( b), center section 691 isfastened to an inside wall of transaxle housing 601H through bolts 651.As shown in FIG. 27, the circular rear top surface of center section691, onto which hydraulic pump P6 is mounted, serves as a pump contactsurface 603. In pump contact surface 603, a right pump kidney port 657 aand a left pump kidney port 657 b are laterally symmetrically openedupward, and a vertical shaft hole 617 n, into which input shaft 617 isrotatably inserted, is opened upward between right and left pump kidneyports 657 a and 657 b. Vertical shaft hole 617 n is passed throughcenter section 691 and also opened downward at the bottom surface ofcenter section 691, as shown in FIG. 30.

As shown in FIGS. 27, 28 and 30, a cylinder block 604 of hydraulic pumpP6 is slidably rotatably fitted onto pump contact surface 603 so as toopen cylinder holes therein to kidney ports 657 a and 657 b, and isnot-relatively rotatably fitted on input shaft 617 passed through shafthole 617 n (in a spline-engaging manner). Pistons 609 are reciprocallyslidably fitted in the respective cylinder holes of cylinder block 604,and project at heads thereof outward from cylinder block 604 so as toabut against movable swash plate P6 a. Input shaft 617 projects upwardfrom cylinder block 604, freely penetrates movable swash plate P6 a, andprojects upward from the top wall of rear transaxle housing 1H so as tobe fixedly provided thereon with pulley 617 a and cooling fan 617 b, asmentioned above. Input shaft 617 inserted in shaft hole 617 n alsoprojects downward from center section 691 into charge pump casing 692 soas to serve as the drive shaft of charge pump 633.

Referring to FIGS. 27 and 28, a fore-and-aft horizontal fluid passagehole 621 (coinciding to fluid passage hole 21 in transaxle 1) interposedbetween hydraulic pump P6 and motor M6 is bored in center section 101,so as to be connected at a rear upper end portion to right pump kidneyports 657 a, and at a front upper end portion thereof to a rear motorkidney port 656 a. In center section 691 is bored therein with a part ofa passage interposed between hydraulic pump P6 and port 601 b(coinciding to passage 27 of transaxle 1) comprising fluid passage holes627 b, 627 d and 627 e. Fluid passage hole 627 e is extended rightwardlydownward from left pump kidney port 657 b to a fore-and-aft intermediateportion of fluid passage hole 627 d. Fluid passage hole 627 d isfore-and-aft horizontally extended under fluid passage hole 621 inparallel. Fluid passage hole 627 b is extended horizontally rightwardfrom a front end portion of fluid passage hole 627 d, and opened outwardat a right side surface of center section 691. Joint plug 627 a providedat the outer end with port 601 b is inserted horizontally leftward intofluid passage hole 627 b through a right sidewall of transaxle housing601H, so as to be fluidly connected to left pump kidney port 657 b.

As shown in FIGS. 27 and 28, the circular front left side surface ofcenter section 291, onto which hydraulic motor M6 is mounted, serves asa motor contact surface 729. In motor contact surface 729, rear motorkidney port 756 a and front motor kidney port 756 b are symmetricallyopened leftward, and a lateral horizontal shaft hole 727 a, into whichmotor shaft 727 is rotatably inserted, is opened leftward between rearand front motor kidney ports 656 a and 656 b.

As shown in FIGS. 27 and 29, a cylinder block 720 of hydraulic motor M6is slidably rotatably fitted onto motor contact surface 729 so as toopen cylinder holes therein to kidney ports 656 a and 656 b, and isnot-relatively rotatably fitted on motor shaft 727 inserted in shafthole 727 a (in a spline-engaging manner). Pistons 723 are reciprocallyslidably fitted in the respective cylinder holes of cylinder block 720,and project at heads thereof outward from cylinder block 720 so as toabut against a fixed swash plate M6 a.

As shown in FIGS. 27 and 29, motor shaft 727, rotatably fitted at aright end portion thereof in shaft hole 727 a of center section 691, isjournalled through a bearing 728 by the partition wall between thehydraulic circuit chamber and the transmission gear chamber, andextended at a left end portion thereof into the transmission gearchamber so as to be provided thereon with a gear 727 b and a brake disc740.

Referring to FIGS. 27 and 28, rear motor kidney port 656 a is connectedto right pump kidney port 657 a through horizontal fluid passage hole(passage) 621, as mentioned above.

Referring to FIGS. 28, 29 and 32(b), a passage interposed betweenhydraulic motor M6 and port 601 a (coinciding to passage 22 of transaxle1) is formed by adapter 693 attached to the bottom surface of centersection 691, horizontal joint plug 622 a screwed into adapter 693, and avertical fluid passage plug 694 fitted into center section 691 throughadapter 693. In this regard, a vertical hole 694 b is bored verticallydownward from front motor kidney port 656 b and downwardly opened at thebottom surface of center section 691. Center section 691 and adapter 693are bored with coaxial vertical bolt holes 695 b and 695 a. Adapter 693is fastened to this bottom surface of center section 691 through avertical bolt 695 screwed into bolt holes 695 a and 695 b. A verticalhole 694 a is bored through adapter 693 so as to be coaxially connectedat the top thereof to hole 694 b in center section 691. Vertical fluidpassage plug 694 is upwardly inserted into hole 694 b through hole 694a. A vertical axial fluid passage hole 622 b is bored in plug 694. Hole622 b is opened at the top of plug 694 in hole 694 b within centersection 691, and opened at a vertical intermediate portion of plugthrough radial horizontal ports into hole 694 a. A lateral horizontaltapped hole is bored in adapter 693 so as to be connected vertical hole694 a and opened rightwardly outward. Joint plug 622 a is screwed fromthe rightward outside of housing 601H into the horizontal tapped hole inadapter 622 a through the right side wall of transaxle housing 601H.Joint plug 622 a includes a horizontal penetrating axial fluid passagehole whose outer right end serves as port 601 a. The fluid passage holein joint plug 622 a is opened at the inward end into hole 694 a so as tobe fluidly connected to vertical fluid passage hole 622 b in plug 694,thereby fluidly connecting port 601 a to motor kidney port 656 b openedto hydraulic motor M6.

Alternatively, adapter 693 may be formed therein with a fluid passagewithout fluid passage plug 694. Alternatively, both fluid passages torespective ports 601 a and 601 b may be formed in adapter 693.Alternatively, adapter 693 may be formed therein with a fluid passage toport 601 b, and a joint plug including port 601 a may be provided ontocenter section 691.

Joint plugs 622 a and 627 a are screwed into the tapped hole in adapter693 and tapped fluid passage hole 627 b, respectively. Alternatively,joint plugs 622 a and 627 a may be screwed in respective tapped holeswithin the wall of transaxle housing 601H, similar to joint plug 22 a(27 a) of FIG. 33( a), or they may be fastened to the outer side surfaceof transaxle housing 601H through a flange, thereby improving the fluidtightness thereof. In either of the two cases, joint plugs 622 a and 627a may be just slidably fitted into the hole in adapter 693 and fluidpassage hole 627 b, respectively (without screwing engagement).

Referring to FIG. 28, center section 691 is bored in a rear portionthereof with a vertical fluid passage hole 634, and provided thereinwith upper and lower charge check valves 635 interposed between fluidpassage hole 634 and respective upper and lower parallel fluid passageholes 621 and 627 d. Each of charge check valves 635 allows only flowfrom fluid from fluid passage hole 634 to corresponding fluid passagehole 21 or 27 d (i.e., prevents backflow to fluid passage hole 634).Fluid passage hole 634 is opened downward at the bottom surface ofcenter section 691, and connected an upwardly opened fluid passage hole699 d bored in charge pump casing 692.

Referring to FIGS. 28, 30, 31(a), 31(b), 32(a) and 32(b), the structurecharge pump 633 and charge pump casing 692 will be described. As shownin FIGS. 32( a) and 32(b), charge pump casing 692 is fastened to centersection through bolts 660. As shown in FIG. 32( a), charge pump casing692 is bored with a vertical circular cylindrical trochoid gear chamber737 which is opened upward to face the bottom surface of center section691. As shown in FIGS. 30 and 32(a), circular (in plan view) shaft hole737 a, into which the lower portion of input shaft 617 is rotatablyinserted, is extended downward from a bottom center portion of trochoidgear chamber 737. Charge pump casing 692 is bored from the bottomsurface of trochoid gear chamber 737 with a vertical suction port 658 aon the left side of shaft hole 737 a, and with a vertical delivery port658 b on the right side of shaft hole 737 a. As shown in FIG. 30, atrochoid gear consisting of an inner gear 735 and an outer gear 736 isdisposed in gear chamber 737. Inner gear 735 is fixed on input shaft 617inserted in shaft hole 737 a, so as to be rotatable integrally withinput shaft 617.

As shown in FIG. 32( a), a fore-and-aft horizontal fluid suction passagehole 631 is bored in charge pump casing 692, connected at a rear endthereof to suction port 658 a, and forwardly outward opened at a recess632 d formed on the front side surface of charge pump casing 692. Ahorizontal fluid filter 632 is fitted at a rear end thereof into recess632 d so as to be fluidly connected to suction passage hole 631.

Referring to FIGS. 30 and 32( a), a lateral horizontal fluid passagehole 698 b is bored in charge pump casing 692, connected at a left endthereof to delivery port 658 b, and connected at a right end thereof toa lateral horizontal joint plug 698 a screwed into charge pump casing692. A right end portion of joint plug 698 a projects rightwardlyoutward from the right side surface of charge pump casing 692, and fromthe right side surface of rear transaxle housing 601H, so as to beprovided with rightwardly outward opened port 675. In this way, apassage (coinciding to passage 98 of transaxle 1) interposed between thedelivery port of charge pump 633 and port 675 is constituted by fluidpassage hole 698 b and joint plug 698 a.

Referring to FIGS. 32( a) and 32(b), a downwardly opened groove ofcharge pump casing 691 and an upwardly opened groove of charge pump 692along a rear side edge of trochoid gear chamber 737 coincide with eachother so as to form a substantially lateral fluid passage hole 699 d.Referring to FIGS. 31( a) and 32(a), a vertical fluid passage hole 699 cis extended downward from a right end portion of fluid passage hole 699d, and connected at the bottom thereof to a lateral horizontal fluidpassage hole 699 b. Fluid passage hole 699 b is opened rightwardlyoutward at the right side surface of charge pump casing 692. Ajoint plug699 a is screwed into fluid passage hole 699 b. A right end portion ofjoint plug 699 a projects rightwardly outward from the right sidesurface of charge pump casing 692, and from the right side surface oftransaxle housing 601H, so as to be provided with rightwardly outwardopened port 676 adjacent to port 675.

Referring to FIGS. 28 and 32( b), the bottom opening of vertical fluidpassage hole 634 is connected to an intermediate portion of fluidpassage hole 699 d. As mentioned above, in center section 691, fluidpassage hole 634 is connected to fluid passage holes 621 and 627 dthrough respective charge check valves 635. In this way, joint plug 699a and fluid passage holes 699 b and 699 c constitute a passage(coinciding to passage 99 of transaxle 1) interposed between port 676and either lower pressurized passage hole 621 or 627 d connected to thesuction side of hydraulic pump P6 through corresponding charge checkvalve 635.

Referring to FIGS. 31( a), 31(b) and 32(a), a check valve 639 isdisposed at a left end portion of fluid passage hole 699 d. A verticalfluid passage hole 636 b is extended downward from an intermediateportion of fluid passage hole 699 d to a relief valve 636. Further, afore-and-aft horizontal drain hole 636 c is extended from relief valve636 and opened outward at the rear side surface of charge pump casing692. Check valve 636 absorbs excessive fluid from fluid passage hole 699d through hole 636 c and drains it to the fluid sump through drain hole636 c. Referring to FIGS. 28 and 31( a), a vertical fluid passage hole650 a is extended downward from fluid passage hole 699 d to a reliefvalve 650. Further, a fore-and-aft horizontal fluid passage hole 650 bis extended from relief valve 650 to delivery port 658 b of charge pump633. Relief valve 650 absorbs excessive fluid from fluid passage hole699 d and supplies it to delivery port 658 b of charge pump. Furtherdescription of check valve 639 and relief valves 636 and 650 is omittedbecause they are similar to respective check valve 39 and relief valves36 and 50 in transaxle 1.

When transaxle 601 replaces rear transaxle 1 in each of the foregoingvehicles 100 to 500, ports 601 a, 601 b, 675 and 676 are disposed on therespective right outer ends of joint plugs 622 a, 627 a, 698 a and 699 aprojecting rightwardly outward from the right side wall of reartransaxle housing 601H. Therefore, pipes 23, 26, 81 and 82 can becompactly collected to be connected to respective ports 601 a, 601 b,675 and 676. Alternatively, for the arrangement of vehicle 100 as shownin FIG. 5, transaxle 601 may be disposed so that ports 601 a, 601 b, 675and 676 are provided on the respective left outer ends of joint plugs622 a, 627 a, 698 a and 699 a projecting leftwardly outward from theleft side wall of rear transaxle housing 601H.

As shown in FIG. 26, front axle-driving hydraulic fluid port 601 a isdisposed higher than rear axle-driving hydraulic fluid port 601 b. Asshown in FIGS. 27 and 32( b), port 601 b is disposed rightward from port601 a. Due to this arrangement of ports 601 a and 601 b, pipes 23 and 27connected to respective ports 601 a and 601 b are can be smoothlyextended forwardly upward without stressing bend, thereby being furthercompactly collected. Front and rear auxiliary (power steering) devicedriving hydraulic fluid ports 675 and 676 are disposed at the sameheight.

A mechanism for controlling the tilt angle and direction of movableswash plate P6 a of hydraulic pump P6, including speed control arm 614,is omitted because it is similar to that of transaxle 1. Additionally,as shown in FIG. 26, transaxle 601 is provided with a shock absorber 614a, pivotally interposed between a tip of speed control arm 614 and aright rear portion of transaxle housing 601H. When depressed speedcontrol pedal 13 is suddenly released from the depression force, shockabsorber 614 a slows down the neutral-returning motion of movable swashplate P6 a, causing abnormal stress onto engine 10 and the travelingpower transmission system, against the neutral-biasing force of a spring(coinciding to spring 115).

In transaxle 601, control lever 614 and center section 691 may beprovided with a mechanism for expanding a neutral dead zone of hydraulicpump P6 relative to the tilt angle of swash plate P6 a similar to themechanism including the orifice members having orifices 171 a, 172 afitted in center section 101 and groove 114 a formed in arm 114 as shownin FIG. 21.

Referring to FIG. 26, transaxle 601 is provided with a forcible reliefvalve mechanism for draining fluid from the HST circuit when the vehicleis towed or for another purpose, similar to that shown in FIG. 19. Inthis regard, as shown in FIG. 26, a forcible relief lever 761 is pivotedon housing 601H so as to operate the forcible relief valve mechanism.

The flow of fluid in HST circuit HC1 (for driving axles 6 and 8 and fordriving power steering cylinder 79) where transaxle 601 replaces reartransaxle 1, whether the vehicle travels forward or backward, is omittedbecause it is similar to the foregoing flow referring to FIG. 2, on theassumption that hydraulic pump P6 with swash plate P6 a and hydraulicmotor M6 serve as hydraulic pump P with swash plate Pa and hydraulicmotor M1, respectively; fluid passage hole 621 serves as passage 21; thefluid passage formed by center section 691, adapter 693 and fluidpassage plug 694 serves as passage 22; joint pipe 627 a and fluidpassage holes 627 b, 627 d and 627 e constitute passage 27; fluidpassage hole 698 b and joint plug 698 a constitute passage 98; jointplug 699 a and fluid passage holes 699 b and 699 c constitute passage99; and suction fluid passage hole 631, fluid filter 632, charge pump633, fluid passage hole 634, check valves 635, relief valve 636, checkvalve 639 and relief valve 650 serve as respective components 31, 32,33, 34, 35, 36, 39 and 50.

The drive train from hydraulic motor M6 to axles 6 in transaxle 601 issimilar to that from hydraulic motor M1 to axles 6 in transaxle 1, onthe assumption that motor shaft 727, gear 727 b, brake disc 740,deceleration gear train 637 and differential gear unit 638 including abull gear 638 a and a differential side gear 638 b serve as respectivecomponents 127, 127 b, 140, 37, 38, 38 a and 38 b. Additionally, intransaxle 601, differential gear unit 638 comprises is provided with adifferential lock mechanism, as shown in FIG. 27. The differential lockmechanism comprises a differential lock pin 638 d and a shifter 638 e.Shifter 638 is manually operated from the outside of transaxle housing601H, so as to slide along (right) axle 6. Differential lock pin 638 dintegrally movably engages with shifter 638 d and is axially slidablyfitted in (right) differential side gear 638 b. When shifter 638 e isoperated for differential locking, shifter 638 e slides (leftward) so asto push differential lock pin 638 d into a hole of bull gear 638 athrough (right) differential side gear 638 b, as shown in FIG. 27,thereby locking (right) axle 6 to bull gear 638 a, whereby left andright axles 6 become rotatable integrally with each other. When shifter638 e is operated for canceling the differential locking, shifter 638 eslides rightward so as to withdraw differential lock pin 638 d from thehole of bull gear 638 b, thereby allowing differential rotation of leftand right axles 6.

It is further understood by those skilled in the art that the foregoingdescription is a preferred embodiment of the disclosed apparatus andthat various changes and modifications may be made in the inventionwithout departing from the spirit and scope thereof defined by thefollowing claims.

1. A hydraulically driven working vehicle comprising: a frame includinga pair of left and right side plates extended in the fore-and-aftdirection of the vehicle; a first transaxle supported by one of frontand rear portions of the frame, the first transaxle including ahydraulic pump, a first hydraulic motor fluidly connected to thehydraulic pump, a first axle driven by the first hydraulic motor, and afirst transaxle housing incorporating the first hydraulic motor and thefirst axle, wherein the first transaxle housing is provided with a pairof outwardly opened first ports fluidly connected to the hydraulic pumpand the first hydraulic motor, respectively; a second transaxlesupported by the other rear or front portion of the frame, the secondtransaxle including a second hydraulic motor fluidly connected to thehydraulic pump, a second axle driven by the second hydraulic motor, anda second transaxle housing supported by the other rear or front portionof the frame, and incorporating the second hydraulic motor and thesecond axle, wherein the second transaxle housing is provided with apair of second ports fluidly connected to the second hydraulic motor; aprime mover supported by the frame between the first and secondtransaxles; a traveling power transmission system supported by the framebetween the prime mover and the first transaxle so as to drivinglyconnect the hydraulic pump to the prime mover; a working device disposedunder the frame between the first and second transaxles; a working powertransmission system supported by the frame between the prime mover andthe working device so as to drivingly connect the working device to theprime mover; and a pair of axle-driving hydraulic pressure fluid pipesinterposed between the pair of first ports and the pair of second portsso as to fluidly connect the second hydraulic motor to the hydraulicpump, wherein the pipes include respective fore-and-aft extendedportions which are extended in the fore-and-aft direction of the vehiclebetween an inside surface of at least one of the left and right sideplates of the frame and the traveling and working power transmissionsystems.
 2. The hydraulically driven working vehicle according to claim1, wherein the fore-and-aft extended portions of both of the pipes areextended along the inside surface of one of the left and right sideplate.
 3. The hydraulically driven working vehicle according to claim 1,wherein the fore-and-aft extended portion of one of the pipes isextended along the inside surface of one of the left and right sideplates, and the fore-and-aft extended portion of the other pipe isextended along the inside surface of the other right or left side plate.4. The hydraulically driven working vehicle according to claim 3, atleast one of the pipes including: a first rigid pipe portion connectedto one of the first ports; a second rigid pipe portion connected to oneof the second ports; and a flexible pipe portion interposed between thefirst and second rigid pipe portions, wherein the flexible hose isextended along one of the left and right side plates of the frame. 5.The hydraulically driven working vehicle according to claim 4, the atleast one of the pipes further including: a swivel joint disposedbetween the flexible pipe portion and at least one of the first andsecond rigid pipe portions.
 6. The hydraulically driven working vehicleaccording to claim 1, at least one of the pipes including: a rigid pipeportion connected to one of the first ports and extended along one ofthe left and right side plates of the frame; and a flexible pipe portioninterposed between the rigid pipe portion and one of the second ports.7. The hydraulically driven working vehicle according to claim 1, thefirst transaxle housing being provided with a pair of outwardly openedthird ports, further comprising: a hydraulic power steering valvedisposed on the frame; and a pair of power steering hydraulic pressurefluid pipes interposed between the hydraulic power steering valve andthe pair of third ports and extended along at least one of theaxle-driving hydraulic pressure fluid pipes.
 8. The hydraulically drivenworking vehicle according to claim 7, wherein the pair of first portsand the pair of third ports are disposed on the same side surface of thefirst transaxle housing.
 9. The hydraulically driven working vehicleaccording to claim 1, the first transaxle, in which the first transaxlehousing incorporates the hydraulic pump, further including: a centersection disposed in the first transaxle housing and interposed betweenthe hydraulic pump and the first hydraulic motor, the center sectionbeing provided with a pair of first and second pump ports fluidlyconnected to the hydraulic pump, a pair of first and second motor portsfluidly connected to the first hydraulic motor, and a passage interposedbetween the first pump port and the first motor port, wherein the pairof first ports are fluidly connected to the second pump port and thesecond motor port, respectively.
 10. The hydraulically driven workingvehicle according to claim 9, the first transaxle further including: acharge pump disposed in the first transaxle housing so as to be driventogether with the hydraulic pump by the power from the prime moverthrough the traveling power transmission system, wherein one of thethird ports is fluidly connected to the charge pump, and wherein theother third port is fluidly connected to a fluid-suction side of thehydraulic pump.
 11. The hydraulically driven working vehicle accordingto claim 10, the first transaxle further including a charge pump casingincorporating the charge pump, the charge pump casing being disposed inthe first transaxle housing and connected to the center section, whereinthe charge pump casing is provided with a passage directly connected tothe pair of third ports.
 12. The hydraulically driven working vehicleaccording to claim 11, wherein the charge pump casing is provided withanother passage directly connected to the pair of first ports so as tofluidly connect the passage in the center section to the pair of firstports.
 13. The hydraulically driven working vehicle according to claim11, further comprising: an adapter attached onto the center section andprovided therein with a passage through which the pair of first portsare fluidly connected to the center section.
 14. A hydraulically drivenworking vehicle comprising: a frame extended in the fore-and-aftdirection of the vehicle; a first transaxle supported by one of frontand rear portions of the frame, the first transaxle including ahydraulic pump, a first hydraulic motor fluidly connected to thehydraulic pump, a first axle driven by the first hydraulic motor, and afirst transaxle housing incorporating the first hydraulic motor and thefirst axle, wherein the first transaxle is formed therein with a firstfluid sump, and wherein the first transaxle housing is provided with apair of outwardly opened first ports fluidly connected to the hydraulicpump and the first hydraulic motor, respectively; a second transaxlesupported by the other rear or front portion of the frame, the secondtransaxle including a second hydraulic motor fluidly connected to thehydraulic pump, a second axle driven by the second hydraulic motor, anda second transaxle housing incorporating the second hydraulic motor andthe second axle, wherein the second transaxle is formed therein with asecond fluid sump, and wherein the second transaxle housing is providedwith a pair of second ports fluidly connected to the second hydraulicmotor; a pair of hydraulic pressure fluid pipes interposed between thepair of first ports and the pair of second ports; a prime moversupported by the frame between the first and second transaxles; atraveling power transmission system supported by the frame between theprime mover and the first transaxle so as to drivingly connect thehydraulic pump to the prime mover; and a reservoir tank fluidlyconnected to the hydraulic pump and the first and second hydraulicmotors, wherein the reservoir tank is disposed so that a fluid level inthe reservoir tank is higher than levels of the first and second fluidsumps.
 15. The hydraulically driven working vehicle according to claim14, wherein the reservoir tank is disposed just behind a rear endsurface of the frame.
 16. The hydraulically driven working vehicleaccording to claim 14, further comprising: a fuel tank joined to thereservoir tank.
 17. The hydraulically driven working vehicle accordingto claim 14, further comprising: a first wheel provided onto the firstaxle; and a second wheel provided onto the second axle, wherein thereservoir tank is disposed between the first and second wheels.